Guides

The concepts behind the converter, explained properly — what Unix time counts, where it breaks, and how to avoid the bugs that follow from getting it wrong.

• What Is Unix Time?

  A single integer that identifies any instant, anywhere on Earth, with no time zone attached. Here is where it came from and what it deliberately leaves out.

• The Year 2038 Problem

  At 03:14:07 UTC on 19 January 2038, a signed 32-bit time_t runs out of room and wraps to 1901. Most systems are fine. The ones that are not are hard to find.

• Seconds vs Milliseconds — The Most Common Timestamp Bug

  Ten digits or thirteen. Get it backwards and your date lands either in January 1970 or somewhere around the year 55,000. Here is how to make the bug impossible.

• ISO 8601 Explained

  The interchange format that removes ambiguity from dates — and the handful of its features you should never use.

• Leap Seconds and Why Unix Time Ignores Them

  Twenty-seven seconds have been inserted into UTC since 1972, and Unix time represents none of them. Usually harmless, occasionally catastrophic.

• UTC vs GMT — What Is the Difference?

  They agree to within a second, which is why the difference is usually ignored — and exactly why it surprises people when it finally matters.

• Daylight Saving Time Bugs and How to Avoid Them

  The missing hour and the repeated hour cause skipped jobs, double charges and impossible timestamps. All of it is preventable by scheduling in UTC.

• Time Zones vs UTC Offsets

  An offset like +05:30 tells you what a clock read. Asia/Kolkata tells you which clock, and what it will read next year. That difference matters for future dates.

• Storing Timestamps in Databases

  The column type you pick determines whether your dates survive a server move, a time zone change and the year 2038. Most defaults are wrong.

• RFC 3339 vs ISO 8601

  Almost the same, but not quite a subset in either direction. If you are writing an API, target the overlap.

• Negative Unix Timestamps and Dates Before 1970

  -86400 is 31 December 1969. Most languages handle it correctly; a surprising number of databases, APIs and validators do not.

• JWT Expiry, Timestamps and Clock Skew

  Pass Date.now() into exp and you have issued a token expiring in the year 56,000. Here is the whole class of timestamp bug around JWTs.

• Cron Jobs and Time Zones

  A job at 02:30 local never runs in spring and runs twice in autumn. The fix is to schedule in UTC and make the job idempotent.

• Notable Unix Timestamps and Epoch Milestones

  1234567890, 2147483647, 1000000000 — the timestamps worth recognising, and the boundaries worth having in your test fixtures.

• Monotonic Clocks — Why You Should Not Subtract Timestamps

  Subtracting two Unix timestamps to measure a duration gives the wrong answer whenever the clock is adjusted — including negative durations.