90 Minute Timer
← All preset timersOne sleep cycle, one feature film, one university lecture, one football match. Ninety minutes keeps turning up as the length of something you sit through in a single go. Sleep is the loosest of those: cycles are commonly described as roughly ninety minutes, but the length varies between people and between cycles across the same night, so timing a wake-up to one is an estimate rather than a calculation. The rest are conventions that hardened into standards. What they share is that ninety minutes is about the longest stretch most people will commit to without expecting an interval in the middle.
Screen kept awake while this runs
Ends with an audible alarm — keep this tab's sound unmuted. A running countdown keeps counting in a background tab and picks itself back up if you reload.
Open this page with the timer already running → — handy as a bookmark, though your device only lets a page make a sound after you have tapped it at least once.
Why 90 minutes
As a work block it holds for the same reason. Ninety minutes is long enough to get past the setting-up phase and finish something, and short enough to schedule twice in one morning. It is also long enough that the timer has to survive being ignored, and this one keeps counting in a background tab through a Web Worker, where a plain browser timer would be throttled and come back several minutes short.
What people set it for
- A deep-work block
- One approximate sleep cycle
- A feature film
- A lecture or seminar
- A football match with half-time
- Long-form exam practice
FAQ
- Is a sleep cycle really ninety minutes?
- Roughly, on average, and not reliably. Ninety minutes is the figure usually quoted, but cycle length differs from person to person and shifts across a night, so a nap set to end at exactly one cycle can still land in the middle of one. Treat it as a sensible guess for a long nap rather than a way to guarantee an easy wake-up.
- Does the countdown keep running when the tab is in the background?
- Yes. It runs in a Web Worker and every tick is derived from a real timestamp, so a backgrounded or throttled tab costs it nothing, which matters most over a long timer where a naive script can return several minutes short. What no page can survive is the machine sleeping, since a sleeping laptop is not running anything at all.
- Does a football match actually last ninety minutes?
- The playing time does, as two halves of forty-five. Elapsed time is always longer, because of a half-time interval of around fifteen minutes and stoppage time added at the end of each half. A ninety-minute timer measures the football rather than the afternoon, so allow closer to two hours if you are timing the whole thing.
