Thirty-five minutes is a class activity with room to demo and room to try. It is also a run or a ride that counts without becoming the whole evening.
Put water in reach. Leaving for the fountain at minute thirty wastes the block and annoys everyone sharing the room. 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 35 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 35 minutes timer on a projector?
Press start, then F or the fullscreen button. Classroom mode hides the writing so the digits fill the wall. Put water in reach. Leaving for the fountain at minute thirty wastes the block and annoys everyone sharing the room.
What is 35 minutes actually good for?
Thirty-five minutes is a class activity with room to demo and room to try.
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.