Ninety minutes is a film period, a long class, or a work block that should include one real break. Decide the break before you start: at forty-five minutes, stand up for five, then continue. Do not 'play it by ear.'
This page is one countdown of ninety. If you want the break enforced, use the Pomodoro timer or the interval timer instead. Press space to start or pause, R to reset, and F for fullscreen. The screen can stay awake after you start, using the wake lock your browser allows. Pick the alarm before you begin. A bell, a chime, a beep, or a short digital pulse all come from the Web Audio API, so there is no sound file to wait on.
This page is the 1 hour 30 minutes countdown and nothing else is running underneath it. Related lengths are linked under the guide if you want a neighbor, and the timer itself stays above the fold.
Questions
How do I run a 1 hour 30 minutes timer on a projector?
Press start, then F or the fullscreen button. Classroom mode hides the writing so the digits fill the wall. This page is one countdown of ninety. If you want the break enforced, use the Pomodoro timer or the interval timer instead.
What is 1 hour 30 minutes actually good for?
Ninety minutes is a film period, a long class, or a work block that should include one real break.
Will the countdown drift if I switch tabs?
No. The end is a timestamp. The display is the gap between that timestamp and now, so a background tab does not lose seconds the way a ticking counter would.