The night with two 1:30ams

At 02:00 the clock goes back to 01:00, and the hour between happens for a second time.

For most people this is an extra hour of sleep and nothing else. For anyone working, travelling or running software through it, it is an hour that exists twice and cannot be told apart.

What it does to a night shift

You work nine hours and get paid for eight, unless somebody has thought about it.

A shift rostered 22:00–06:00 spans the repeated hour, so the actual elapsed time is nine hours. In spring the same shift is seven hours, because an hour is missing.

Most employers handle this — many pay actual hours worked, some rotate who takes which night — but it is worth knowing which policy applies to you before the night rather than after. It is also worth checking that a rota built as "eight hour blocks" in local time still tiles the whole night on both transition dates.

What it does to logs and software

This is where the repeated hour is genuinely dangerous, because the failure is silent.

Timestamps become ambiguous. "01:30" that night refers to two instants an hour apart. If your logs record local time, events from that window cannot be correctly ordered — and merging two systems' logs across it can produce a sequence that appears to violate causality.

Scheduled jobs can run twice. Anything defined in local time that fires at 01:30 will fire in both instances of it. If that job sends emails, charges cards, or moves money, it does it twice.

In spring, the opposite: a job scheduled at 02:30 never runs at all, because that time does not occur.

The fix is the same in both directions: define schedules and store timestamps in UTC. UTC has no transitions. Convert to local time only for display, at the last possible moment.

What it does to alarms

Phones handle it correctly. Set an alarm for 06:00 and it goes off at 06:00 on the new clock, which is what you want.

The failures are the manual ones — an alarm clock that does not update itself, a hotel wake-up call taken by someone who had not thought about it, a device with a stale time zone database. If you have an early flight the morning after a transition, this is the one to double-check.

And the spring version is worse than the autumn one: losing an hour before a 05:00 departure is a genuinely bad start.

What it does to you

The autumn change is the easy one. You gain an hour, most people sleep a little more, and the adjustment takes a day or two.

The spring change is the one with measurable consequences: studies have consistently found a short-lived rise in traffic accidents and cardiac events in the days after clocks go forward. An hour of lost sleep across a whole population is not nothing.

When

This year the clocks go back on 2026-10-25 in the UK and EU, and on 2026-11-01 in the US. In Australia they went back on 2026-04-04.

If you work nights, run scheduled systems, or fly early — those are the dates to look at in advance.

Related: The clock change: what happens at 2am · When does daylight saving time end?

Figures on this page are computed from the IANA time zone database. Last generated 2026-08-18.