A recurring local time is not a recurring instant.

02:30 on 8 March 2026 in New York does not exist — the clock goes from 01:59 straight to 03:00, so a job scheduled there has no instant to run at. 01:30 on 1 November exists twice, at 05:30Z and 06:30Z, an hour apart — so a job scheduled there runs twice. Neither date is in the schedule, and both are exact.

The engine is free and needs no account, and it reads the full IANA database out of your own browser — nothing is fetched and nothing is vendored. A time difference is not a number, it is a list of runs: New York to London is 5 hours for 337 days of 2026 and 4 hours for 28, in two separate windows, because the US and the EU change on different Sundays. Across the equator it is worse — New York to Sydney takes three distinct values, because the two zones transition in opposite directions. Adding 24 hours is not adding a day: a 09:00 job advanced by 86,400,000 milliseconds becomes a 10:00 job and stays one. And EST is not a place — it is a fixed −05:00 that never springs forward, while CST resolves to a zone that does. Every lane ships a worked example that costs nothing. Writing the report needs credits.