A plank timer

This page starts counting 3 minutes the moment it opens, and makes a sound when it finishes. Nothing to set, and nothing to press first.

What people set 3 minutes for

Holding a plank to a set time instead of to the point of collapse.

Worth knowing

Timing a hold rather than counting one turns it into something repeatable — you can tell next week whether you actually improved.

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.