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title Timing of DST Jumps

Time zones that use daylight saving time (DST) vary about when they implement the time jumps. You shouldn't assume that the rules you're familiar with from a local time zone translate to other zones.

One difference that often catches out developers is that some zones change clocks at midnight. A good example comes from Jordan (Asia/Amman) in 2021:

  • One second after 2021-03-25 23:59:59 was 2021-03-26 01:00:00 (DST started).
  • One second after 2021-10-29 00:59:59 was 2021-10-29 00:00:00 (DST stopped).

This creates the situation where midnight at the start of March 26 didn't happen, while midnight on October 29 happened twice.

Moment Timezone accounts for these oddities as described in the "Parsing Ambiguities" documentation. But applications can still have bugs when they make other assumptions about time jumps, especially regarding the start of a day. So be aware that a day doesn't always start at midnight.