A ninety minute timer

This page starts counting 90 minutes the moment it opens, and makes a sound when it finishes. Nothing to set, and nothing to press first.

What people set 90 minutes for

A full sleep cycle, a film, a deep-work block, or a football match without stoppages.

Worth knowing

Ninety minutes is roughly one human sleep cycle, so waking at a multiple of it tends to feel better than waking a fixed eight hours after going to bed.

Questions

Do the timers keep running if I switch tabs?

Yes. The countdown is measured against a monotonic clock rather than counted in ticks, so a backgrounded tab, a throttled timer or a laptop lid closing does not lose time — when you come back it shows what it should, not what it managed to count.

Does a timer survive a daylight-saving change?

Yes, and the distinction matters. A countdown measures elapsed real time, so a timer set for six hours across a spring-forward still runs six real hours even though the wall clock advances seven. An alarm set for a wall-clock time does the opposite: it fires when the clock says so, which is what you want from an alarm.