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TimeShift: World Clocks, Meeting Planner & Timestamp Decoder — All in Your Browser

Milan SalviMar 26, 202615 min readTools
TimeShift: World Clocks, Meeting Planner & Timestamp Decoder — All in Your Browser

Table of Contents

  1. What Is TimeShift?
  2. 300+ IANA Time Zones via Intl API
  3. The Converter: DST-Aware Time Zone Translation
  4. World Clock: Live Updating City Dashboard
  5. Meeting Planner: Find Overlapping Work Hours
  6. The Overlap Algorithm Explained
  7. Timestamp Tools: Unix, ISO 8601, RFC 2822
  8. Batch Conversion: Process 10,000 Rows
  9. ICS Calendar Export & URL Sharing
  10. How DST Is Handled (Intl.DateTimeFormat)
  11. Privacy: Zero Data Transmission
  12. Common Use Cases
  13. TimeShift vs. World Time Buddy, Every Time Zone & TimeAndDate.com
  14. Frequently Asked Questions
  15. Conclusion

Time zones are one of the most deceptively complex problems in software. There are over 300 of them. They shift by different amounts at different times of year. Governments change their rules with little notice — sometimes with just weeks of lead time. Daylight Saving Time transitions happen on different dates in different countries, and some countries skip DST entirely while others have abandoned it mid-decade. Abbreviations like "EST" are ambiguous (it means Eastern Standard Time in both the US and Australia, but they are 16 hours apart). And yet, every distributed team, every international traveler, every developer parsing log files, and every remote worker scheduling a call across continents needs to deal with this complexity daily. The TimeShift converter on ZeroDataUpload tackles the full breadth of this problem: five specialized tabs covering time conversion, world clocks, meeting planning, timestamp decoding, and batch processing — all running entirely in your browser with zero data uploads and zero external date libraries.

1. What Is TimeShift?

TimeShift is a comprehensive time zone utility organized into five tabs, each addressing a distinct aspect of time zone work:

The entire application is built on the browser's native Intl.DateTimeFormat API — no Moment.js, no Luxon, no date-fns, no external date library of any kind. This is a deliberate architectural decision with profound implications for accuracy, maintenance, and privacy, as we will explore in detail throughout this article.

2. 300+ IANA Time Zones via Intl API

TimeShift accesses the full IANA Time Zone Database through a single line of modern JavaScript: Intl.supportedValuesOf('timeZone'). This method, available in all modern browsers, returns every time zone identifier that the browser's internationalization engine recognizes — typically 300 to 400 zones depending on the browser and its version of the IANA database.

The IANA Time Zone Database (often called the "tz database" or "Olson database," after its original maintainer Arthur David Olson) is the authoritative global registry of time zone rules. It uses a Continent/City naming convention where each identifier refers to the most populous city in that zone's region: America/New_York, Europe/London, Asia/Tokyo, Australia/Sydney. This convention is critical because it avoids the ambiguity of abbreviations. "EST" could mean UTC-5 (Eastern Standard Time in the US) or UTC+10 (Eastern Standard Time in Australia). "CST" is shared by Central Standard Time (US), China Standard Time, and Cuba Standard Time. "IST" means India Standard Time, Israel Standard Time, or Irish Standard Time depending on who is speaking. IANA identifiers eliminate this ambiguity entirely.

TimeShift extracts human-readable city names from IANA identifiers using a straightforward parsing strategy: split the identifier by /, take the last segment, and replace underscores with spaces. So America/New_York becomes "New York," Asia/Ho_Chi_Minh becomes "Ho Chi Minh," and Pacific/Port_Moresby becomes "Port Moresby." The tool also handles historical IANA renames gracefully — the database has renamed several zones over the years (Calcutta became Kolkata, Saigon became Ho Chi Minh, Rangoon became Yangon), and modern browsers return the current names.

For quick access, TimeShift provides 32 popular zones that appear at the top of every zone selector dropdown, separated from the full alphabetical list. These 32 zones cover the most commonly needed conversions:

This curated list handles the vast majority of real-world conversion needs — the time zones of global business hubs, major tech centers, and the most common origin/destination pairs for international calls. The full 300+ zone list is always available for the less common cases: Pacific island nations, historical zones, or regions with unusual offset increments like UTC+5:30 (India), UTC+5:45 (Nepal), or UTC+9:30 (Central Australia).

3. The Converter: DST-Aware Time Zone Translation

The Converter tab is TimeShift's primary interface and it handles the most fundamental time zone task: given a date, a time, and a source zone, what is the equivalent time in a target zone? The interface provides a date picker, a time picker, a "From" zone selector, and a "To" zone selector. Selecting any combination immediately produces the converted time along with the UTC offset of each zone and the time difference between them.

The conversion engine uses Intl.DateTimeFormat with the timeZone option to perform the actual calculation. Here is the conceptual flow: TimeShift constructs a JavaScript Date object representing the selected date and time in the source time zone, then formats that same instant using the target time zone. Because Intl.DateTimeFormat is DST-aware — it consults the IANA database embedded in the browser to determine whether DST is active for a given zone on a given date — the conversion automatically accounts for DST transitions without any manual offset tables or hardcoded rules.

The offset display uses a helper function called getUtcOffset() that leverages the timeZoneName: 'shortOffset' option to extract a formatted offset string like "GMT-5" or "GMT+5:30" directly from the Intl API. A companion function, getLongOffset(), calculates the offset in total minutes by formatting the date in both UTC and the target zone, parsing the results, and computing the difference. This minute-based offset is used for the difference calculation displayed between the two zones — for example, "New York is 13 hours behind Tokyo" or "London is 5.5 hours behind Kolkata."

A swap button between the From and To zone selectors reverses the direction of conversion with a single click. If you were converting from America/New_York to Asia/Tokyo, clicking swap changes it to Asia/Tokyo to America/New_York and recalculates immediately. The converted result, offset display, and difference calculation all update in real time as you change any input.

4. World Clock: Live Updating City Dashboard

The World Clock tab displays a grid of city clocks that update every second via a setInterval(1000) timer. Each clock card shows the city name (extracted from the IANA identifier), the current time formatted with hours, minutes, and seconds, the current date, the UTC offset, and a day/night indicator. The day/night logic is straightforward: TimeShift calls getHourInTz() to determine the current hour (0-23) in that zone, and any hour from 6 through 21 (inclusive — meaning 6:00 AM to 9:59 PM) is classified as daytime and displays a sun indicator, while hours 0 through 5 and 22 through 23 display a moon indicator.

By default, the World Clock loads with four cities: New York, London, Tokyo, and Sydney. These defaults were chosen because they span four major economic regions across a roughly even distribution of the 24-hour clock. But the World Clock is fully customizable. Clicking the "Add City" button opens a modal with a searchable list of all 300+ IANA zones. Type a city name, select it, and a new clock card appears in the grid. Each card also has a remove button to delete it from the display.

Your city selections are persisted in localStorage under the key tz-world-clocks. When you reload the page or return to TimeShift later, your custom set of clocks is restored exactly as you left it. This persistence means the World Clock effectively becomes your personal time dashboard — add the cities where your team members, clients, or family live, and you have a permanent at-a-glance view of what time it is everywhere that matters to you.

The live update mechanism is designed for performance. Rather than destroying and recreating DOM elements every second, TimeShift performs text-only updates to the existing clock card elements. The setInterval callback iterates through the active clocks, calls Intl.DateTimeFormat with each clock's time zone to get the current formatted time, and updates the textContent of the time, date, and day/night indicator elements. This approach avoids layout thrashing, minimizes garbage collection pressure, and keeps the update cycle well under one millisecond even with dozens of clocks displayed simultaneously.

5. Meeting Planner: Find Overlapping Work Hours

The Meeting Planner tab solves one of the most common distributed-team headaches: finding a time when everyone can meet during their normal work hours. The interface lets you add multiple time zones as "chips" — clickable labels that represent each participant's location. For each zone chip, you select a work hours range with configurable start times (6 AM through 10 AM) and end times (4 PM through 8 PM). These flexible ranges acknowledge that "work hours" vary by culture, role, and personal preference — a developer in Berlin might start at 10 AM, while a trader in Hong Kong starts at 6 AM.

Once you have added two or more zones with their work hours configured, TimeShift renders a 24-hour timeline table with UTC hours (0 through 23) as columns and your selected zones as rows. Each cell is color-coded to represent the status of that hour in that zone:

The overlap hours are highlighted prominently and listed explicitly below the table for each zone, showing what the overlapping UTC hours translate to in local time. You can copy the overlap hours for any zone with a single click. If at least one overlap hour exists, TimeShift offers an ICS calendar export button that creates a calendar event starting at the first overlap hour, making it trivial to schedule the meeting directly from the planner.

6. The Overlap Algorithm Explained

The overlap calculation is the algorithmic heart of the Meeting Planner, and understanding it reveals why time zone intersection is harder than it first appears. Here is the step-by-step process:

Step 1: Convert local work hours to UTC for each zone. For each zone, TimeShift takes the configured work start and end hours (expressed in local time) and converts them to UTC hours. If a zone is at UTC+5:30 (India) and the work hours are 9 AM to 6 PM local, then the UTC equivalent is 3:30 AM to 12:30 PM UTC. If a zone is at UTC-5 (New York during EST) with work hours of 9 AM to 5 PM local, the UTC equivalent is 2 PM to 10 PM UTC. This conversion uses the same Intl.DateTimeFormat-based offset calculation that powers the Converter tab, so it is fully DST-aware — the UTC mapping shifts automatically when a zone enters or exits Daylight Saving Time.

Step 2: Build a set of "work" UTC hours for each zone. Each zone's converted work range is expanded into a set of discrete UTC hours. For New York (2 PM to 10 PM UTC), the set is {14, 15, 16, 17, 18, 19, 20, 21}. For India (3:30 AM to 12:30 PM UTC), the set is {4, 5, 6, 7, 8, 9, 10, 11, 12} — note that half-hour offsets mean the set starts at hour 4 (the first full UTC hour within the range) rather than hour 3. This discretization to whole hours is a practical simplification that matches how meetings are actually scheduled.

Step 3: Compute the intersection of all zone sets. The overlap hours are the UTC hours that appear in every zone's work set. This is a straightforward set intersection: iterate through UTC hours 0 to 23, and for each hour, check whether it falls within the work range of every zone. If any zone does not have that hour in its work set, it is not an overlap hour. Only hours that pass the test for all zones are marked as overlap.

Step 4: Map overlap UTC hours back to local time per zone. Once the overlapping UTC hours are identified, TimeShift converts each one back to local time for each zone. This produces the final output: "The overlap is 2 PM - 4 PM UTC, which is 9 AM - 11 AM in New York, 2 PM - 4 PM in London, 7:30 PM - 9:30 PM in Mumbai, and 11 PM - 1 AM in Tokyo."

The elegance of this algorithm is that it scales linearly with the number of zones. Adding a fifth or sixth zone does not make the calculation exponentially harder — it just adds one more set to the intersection. The practical effect, however, is that more zones generally mean fewer overlap hours. With two zones, you might have 4-6 overlap hours. With four zones spanning the globe, you might have 1-2 hours or even zero. The Meeting Planner makes this tradeoff visible at a glance through the color-coded timeline.

When Overlap Is Zero

If your team spans time zones that are 12+ hours apart (say, New York and Sydney), the Meeting Planner may find zero overlap during standard work hours. In that case, consider widening the work hour ranges — setting New York's start to 7 AM and Sydney's end to 8 PM might open a 1-hour window. The flexible start/end selectors are specifically designed for this scenario.

7. Timestamp Tools: Unix, ISO 8601, RFC 2822

The Timestamps tab addresses a different audience: developers, system administrators, and data engineers who work with machine-readable time formats daily. The tab is divided into two sections: a live display of the current time in six formats, and a decoder that converts any timestamp into all formats simultaneously.

The six live formats are:

All six displays update in real time as the seconds tick by. The Unix timestamps increment by 1 (or 1000 for milliseconds) every second. The ISO and RFC strings update their seconds field. The human readable string updates its time component. This live display is invaluable for developers who need to quickly grab the current timestamp in a specific format — click copy on the Unix seconds display and paste it into a database query, an API request, or a log file search.

The Decoder section accepts any timestamp string in an input field and auto-detects its format. A 10-digit number is interpreted as Unix seconds. A 13-digit number is interpreted as Unix milliseconds. A string containing "T" and "Z" or an offset pattern is parsed as ISO 8601. Other date-like strings are attempted with the native Date constructor. Once parsed, the decoded time is displayed in all six formats simultaneously, along with a relative time indicator — "5 minutes ago," "3 hours from now," "2 days ago" — that gives you immediate human context for what the timestamp represents.

8. Batch Conversion: Process 10,000 Rows

The Batch tab is designed for bulk operations — converting an entire dataset of timestamps from one zone to another in a single operation. This is a scenario that arises frequently in data engineering: you receive a CSV export from a system that stores times in UTC, and you need all timestamps in your local zone for a report. Or you are merging datasets from servers in different regions and need to normalize everything to a single zone.

The workflow is straightforward: upload a CSV or TXT file, and TimeShift auto-detects whether the first row contains headers. It then identifies the first column that contains date/time values by sampling rows and attempting to parse them. You select the source time zone ("what zone is this data in?") and the target time zone ("what zone do I want?"), then click convert.

TimeShift processes each row by parsing the date/time value from the detected column, constructing a JavaScript Date object, and formatting it in the target time zone using Intl.DateTimeFormat. The tool handles three input formats: Unix timestamps (both 10-digit seconds and 13-digit milliseconds), ISO 8601 strings (with or without timezone suffixes), and general date strings parseable by the Date constructor. If a row's date value cannot be parsed, the output shows "PARSE ERROR" for that row rather than silently failing or crashing the entire batch.

The output is rendered as a table with three columns: the original value, the converted value, and the UTC offset that was applied. You can download the complete result as a CSV file. The tool handles up to 10,000 rows, which covers the vast majority of real-world batch conversion scenarios — log files, transaction exports, scheduling databases, sensor data dumps, and analytics reports.

Batch Performance

Processing 10,000 rows is computationally intensive, but because Intl.DateTimeFormat is implemented in native browser code (written in C++ as part of the JavaScript engine's ICU integration), it executes significantly faster than any JavaScript date library could. TimeShift can convert 10,000 timestamps in under 2 seconds on a modern machine — each conversion is essentially a native function call rather than interpreted JavaScript arithmetic.

9. ICS Calendar Export & URL Sharing

TimeShift supports two sharing mechanisms that extend its utility beyond the immediate conversion: ICS calendar file exports and shareable URLs.

ICS Calendar Export — The Converter tab and the Meeting Planner tab both offer the ability to download an ICS (iCalendar) file. ICS is the universal calendar interchange format supported by Google Calendar, Apple Calendar, Outlook, Thunderbird, and virtually every calendar application in existence. When you click the ICS export button, TimeShift generates a file with the following structure:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//ZeroDataUpload//TimeShift//EN
BEGIN:VEVENT
DTSTART:20260326T140000Z
DTEND:20260326T150000Z
SUMMARY:Converted Time Event
DESCRIPTION:Converted from America/New_York to Asia/Tokyo
END:VEVENT
END:VCALENDAR

The DTSTART and DTEND values are in UTC (indicated by the "Z" suffix), ensuring the event appears at the correct local time regardless of which calendar application or device opens the file. The SUMMARY provides a descriptive title, and the DESCRIPTION includes the source and target zones for reference. In the Meeting Planner, the ICS export creates an event starting at the first overlap hour — this lets you jump straight from identifying the best meeting time to putting it on everyone's calendar.

Shareable URL — The Converter tab encodes the current conversion state into URL query parameters: from, to, date, and time. Clicking the share button copies a URL like https://timezone.zerodataupload.com/?from=America/New_York&to=Asia/Tokyo&date=2026-03-26&time=14:00 to your clipboard. When someone opens this URL, TimeShift pre-fills all fields and shows the conversion result immediately. This is invaluable for asynchronous communication: instead of writing "the meeting is at 2 PM New York time, can you check what that is in your zone?", you paste a link that shows the answer directly.

10. How DST Is Handled (Intl.DateTimeFormat)

Daylight Saving Time is the single greatest source of time zone bugs in software. The rules are Byzantine: the US transitions on the second Sunday of March and the first Sunday of November. The EU transitions on the last Sundays of March and October. Australia transitions on the first Sunday of April and the first Sunday of October — but only in some states (Queensland does not observe DST). Brazil abandoned DST in 2019. Morocco observes DST but suspends it during Ramadan. Iran transitions on the March equinox. And these rules change — the EU has been debating the abolition of DST since 2019, and any member state could exit the system.

Most time zone libraries handle DST by shipping a compiled copy of the IANA database as a JavaScript data file. Moment.js with moment-timezone ships a 40KB+ JSON blob of zone rules. Luxon relies on Intl at runtime (similar to TimeShift) but still bundles significant overhead for its API surface. date-fns-tz bundles zone data for specific regions. The fundamental problem with shipped data is that it goes stale. When Turkey announced in 2016 that it would stay on permanent summer time (UTC+3) year-round, applications using bundled zone data needed a library update to reflect the change. Those that did not update continued showing the wrong time for Turkish zones until their next dependency refresh.

TimeShift sidesteps this entire category of problems by relying exclusively on the Intl.DateTimeFormat API, which delegates to the IANA database embedded in the operating system and browser. When a government changes its DST rules, the IANA maintains the canonical database, operating system vendors (Microsoft, Apple, Google) push updates, and browsers inherit the changes automatically through OS updates and browser releases. TimeShift's code does not need to change at all — the next time a user's browser updates, the new rules take effect. There is no data file to keep in sync, no dependency to bump, no deployment to push.

This architecture has three key advantages:

The browser is not just running TimeShift's code — it IS the time zone engine. Every modern browser ships a complete, up-to-date copy of the IANA database as part of its internationalization subsystem. TimeShift simply asks the browser: "What time is it in Asia/Tokyo on March 26, 2026 at 2:00 PM New York time?" The browser does the rest.

11. Privacy: Zero Data Transmission

Time zone conversions can be surprisingly revealing. The zones you convert between suggest where you live and where your contacts are. The specific times you check hint at meeting schedules, travel itineraries, or business relationships. Batch conversions might contain timestamps from internal systems, server logs, or transaction records. A timestamp decoder query might reveal the exact time something happened in your infrastructure.

TimeShift processes everything client-side. There are no API calls for time zone data — it all comes from the browser's built-in Intl subsystem. There is no server receiving your conversion queries. There is no analytics system beyond Google Analytics (which tracks page visits, not conversion content). The only data persisted is your World Clock city selections, stored in localStorage under the key tz-world-clocks on your device and nowhere else.

When you upload a CSV file for batch conversion, the file is read by JavaScript's FileReader API directly in your browser. The file's contents are parsed, converted, and displayed without ever leaving your machine. When you download the converted CSV, it is generated client-side as a Blob and served through a URL.createObjectURL link. The original file, the parsed data, the converted results, and the downloaded output — every step happens in browser memory. No temporary server storage, no cloud processing, no data pipeline to audit.

This is especially important for the batch conversion use case, where organizations might be converting timestamps from internal databases, application logs, or financial transaction records. Uploading such data to an online converter would mean sending potentially sensitive operational data to a third-party server. With TimeShift, the data stays on your device — period.

12. Common Use Cases

TimeShift's five tabs cover a remarkably wide range of practical scenarios:

Remote Teams & Distributed Companies — The Meeting Planner is purpose-built for this. A team with members in San Francisco, London, and Bangalore can find overlap hours in seconds. The World Clock provides a permanent dashboard of team locations. The URL sharing feature lets a manager send a link that says "here is the proposed time" in each recipient's local zone.

International Travelers — The Converter handles the basic "what time will it be when I land?" question, with DST-awareness ensuring accuracy even for trips that cross a DST transition date. The World Clock can be configured to show your home city alongside your destination, so you always know what time it is back home.

Software Developers — The Timestamp tab is a daily tool for developers working with APIs, databases, and log files. Decode a Unix timestamp from a production log. Convert an ISO 8601 string from an API response. Check whether a 10-digit number is a Unix timestamp or an ID. The batch converter handles the "all our server logs are in UTC and the incident report needs to be in local time" scenario.

Data Analysts & Engineers — Batch conversion of CSV files containing timestamps from different systems. A common pattern is merging data from US servers (storing in America/New_York) with data from European servers (storing in Europe/Berlin) — normalize everything to UTC or a single local zone.

Event Organizers & Content Creators — Scheduling webinars, live streams, or product launches that need to be announced across multiple time zones. The Converter's URL sharing produces a link that shows the event time in the recipient's zone, reducing confusion and no-shows.

Freelancers & Consultants — Working across time zones means coordinating with clients in different regions. The Meeting Planner finds mutually acceptable call times. The ICS export puts the meeting directly on the calendar.

13. TimeShift vs. World Time Buddy, Every Time Zone & TimeAndDate.com

The time zone tool space is crowded, but most tools make significant tradeoffs that TimeShift avoids. Here is how the major alternatives compare:

World Time Buddy — WTB is one of the most popular time zone comparison tools on the web. It displays a horizontal timeline for multiple zones with color-coded work hours and lets you slide a time cursor to see the equivalent time across all zones. However, World Time Buddy operates on a freemium model: the free tier is limited to 4 zones and displays advertising. Adding more zones, removing ads, and accessing features like calendar integration require a paid subscription ($3.99/month or $24/year). WTB also runs server-side — your zone selections, comparison queries, and usage patterns are processed on their infrastructure. TimeShift provides unlimited zones, zero advertising, calendar export (ICS), and a full meeting planner with overlap calculation — all free, all client-side.

Every Time Zone — ETZ is a beautifully designed single-page tool by the team at Basecamp (now 37signals). It displays a horizontal timeline with colored bars representing zones and uses a vertical line to show the current time. The design is elegant and the tool is genuinely pleasant to use. However, Every Time Zone is deliberately minimal: it does not offer a meeting planner with overlap calculation, has no timestamp decoder, does not support batch conversion, cannot export ICS files, and has no URL sharing for specific conversions. It is a visualization tool, not a conversion toolkit. If you need to see time zones at a glance, ETZ is excellent. If you need to actually do something with that information — schedule a meeting, decode a timestamp, convert a CSV — you need TimeShift.

TimeAndDate.com — TimeAndDate.com is the encyclopedia of time zone tools. It has a world clock, a meeting planner, a time zone converter, an event countdown, a duration calculator, a calendar generator, and dozens of other date/time utilities. The depth of content is genuinely impressive. The tradeoffs are significant, though: the site is extremely heavy with advertising (multiple display ads, pop-ups, and interstitials), the interface is dense and cluttered by modern standards, many features require multiple page loads (each generating fresh ad impressions), and the site processes everything server-side. A simple conversion query on TimeAndDate.com transmits your source zone, target zone, date, and time to their servers, where it is processed and the result is sent back as a new HTML page. TimeShift offers the same core functionality — converter, world clock, meeting planner, timestamps — in a clean, ad-free, single-page application that processes everything locally.

The pattern is consistent across all three competitors: they either limit functionality behind a paywall (World Time Buddy), optimize for simplicity at the expense of utility (Every Time Zone), or maximize content and advertising at the expense of user experience and privacy (TimeAndDate.com). TimeShift occupies a unique position: full-featured, ad-free, and private.

14. Frequently Asked Questions

How many time zones does TimeShift support?

TimeShift supports every time zone recognized by your browser's Intl API, which is typically 300 to 400 zones depending on the browser version. This includes all IANA Time Zone Database entries — every country, every historical zone, and every unusual offset like UTC+5:45 (Nepal) or UTC+8:45 (Western Australia's unofficial Eucla time). Additionally, 32 popular zones are highlighted at the top of every selector for quick access.

Does TimeShift handle Daylight Saving Time automatically?

Yes. TimeShift uses the browser's native Intl.DateTimeFormat API, which consults the IANA database embedded in your operating system. When you convert a date that falls during a DST transition period, the correct offset is applied automatically. For example, converting "March 15, 2026 at 2:00 PM" from New York to London will correctly show the 5-hour difference (EDT to BST), not the 4-hour or 6-hour difference you would get if DST were ignored.

What is the IANA Time Zone Database?

The IANA Time Zone Database (also called the tz database or Olson database) is the global authority on time zone rules. Maintained by a community of volunteers under the Internet Assigned Numbers Authority, it catalogs every time zone rule change since the adoption of standard time in the 19th century. It uses the Continent/City naming convention (e.g., America/New_York) to avoid the ambiguity of abbreviations like EST or CST. The database is updated 3-10 times per year as governments change their rules.

Why not use EST, PST, or other abbreviations?

Because they are ambiguous. "EST" means UTC-5 in the United States but UTC+10 in Australia. "CST" is used by the US (UTC-6), China (UTC+8), and Cuba (UTC-5). "IST" refers to India (UTC+5:30), Israel (UTC+2), or Ireland (UTC+1). IANA identifiers like America/New_York or Australia/Sydney are globally unique and unambiguous. TimeShift uses IANA identifiers internally and displays city names for readability.

What timestamp formats does the decoder accept?

The decoder auto-detects four categories: 10-digit numbers are interpreted as Unix timestamps in seconds (e.g., 1711468200). 13-digit numbers are interpreted as Unix timestamps in milliseconds (e.g., 1711468200000). ISO 8601 strings with the "T" separator and optional "Z" or offset suffix are parsed directly (e.g., 2026-03-26T14:30:00Z). All other strings are attempted with the JavaScript Date constructor, which handles a wide range of date formats including RFC 2822.

Can I convert more than 10,000 rows in batch mode?

The 10,000-row limit is a practical safeguard. Processing more rows could cause browser tab freezing or memory issues, especially on mobile devices. For datasets larger than 10,000 rows, split your CSV into multiple files and process them sequentially. Each output CSV can be concatenated afterward since the column format is consistent across all batch runs.

How does the Meeting Planner determine work hour overlap?

The planner converts each zone's configured work hours (e.g., 9 AM to 5 PM) into UTC hour ranges. It then computes the set intersection of all zones' UTC work hours. The resulting hours are the times when every participant is simultaneously within their defined work range. The overlap is displayed both on the UTC timeline table and as local times for each zone.

What does the ICS export contain?

The ICS file is a standard iCalendar event with a DTSTART and DTEND in UTC, a summary title, and a description noting the source and target zones. It is compatible with Google Calendar, Apple Calendar, Microsoft Outlook, and any other application that supports the iCalendar standard. From the Converter, it exports the converted time as a 1-hour event. From the Meeting Planner, it exports the first overlap hour.

Does TimeShift store any data on a server?

No. TimeShift has no backend server. All conversions happen in your browser using the native Intl API. The only data stored anywhere is your World Clock city selections in localStorage (key: tz-world-clocks), which is on your device. Uploaded CSV files for batch conversion are read into browser memory, processed, and never transmitted. Your conversion queries, timestamps, and meeting planner configurations exist only in your browser tab and disappear when you close it.

Why does TimeShift not use Moment.js or another date library?

Modern browsers ship with a complete, authoritative implementation of the IANA Time Zone Database via the Intl.DateTimeFormat API. Using an external library would mean bundling a duplicate copy of zone data (adding 40KB+ to the download), maintaining a dependency that needs updates whenever IANA publishes new rules, and introducing a layer of JavaScript interpretation between the conversion request and the native timezone engine. By using Intl directly, TimeShift is smaller, faster, always current, and has zero dependency risk. The Intl approach is also recommended by the Moment.js team themselves, who declared Moment.js a legacy project in 2020 and recommend native alternatives for new projects.

15. Conclusion

Time zone complexity is not going away. As long as the Earth rotates, governments set clocks, and people collaborate across borders, there will be a need to convert times, find meeting overlaps, decode timestamps, and process date columns in CSV files. The question is not whether you need a time zone tool — it is whether the tool you use respects your time, your data, and your intelligence.

TimeShift brings five specialized capabilities into a single browser tab: a DST-aware converter with ICS export and URL sharing, a live world clock dashboard with per-second updates and persistent customization, a meeting planner that algorithmically finds work hour overlap across any number of zones, a timestamp toolkit that speaks Unix, ISO 8601, and RFC 2822 fluently, and a batch processor that can convert 10,000 rows of CSV data without your file ever leaving your machine. It does all of this with zero external date libraries by leveraging the browser's native Intl.DateTimeFormat API — an approach that guarantees current DST rules, native execution speed, and zero bundle overhead.

No accounts. No advertisements. No server-side processing. No data transmission. Just open TimeShift, convert your times, and close the tab. The time zones are complicated enough — the tool should not be.

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Milan Salvi

Milan Salvi

Founder, Leena Software Solutions

Milan is the founder of ZeroDataUpload and Leena Software Solutions, building privacy-first browser tools that process everything client-side. View all articles · About the author.

Published: March 26, 2026