Twenty-eight minutes is four sevens, a circuit with equal stations and no station long enough to bore anyone. It also fits a short lecture plus questions if you keep the questions inside the timer.
Start it when the work starts, not when the shuffling stops. Shuffling expands to fill whatever you give it. 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 28 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 28 minutes timer on a projector?
Press start, then F or the fullscreen button. Classroom mode hides the writing so the digits fill the wall. Start it when the work starts, not when the shuffling stops. Shuffling expands to fill whatever you give it.
What is 28 minutes actually good for?
Twenty-eight minutes is four sevens, a circuit with equal stations and no station long enough to bore anyone.
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.