Seventeen minutes is long enough to get into a task and short enough that you can see the far side. Use it when twenty would spill into a meeting. The odd minute keeps the block from feeling like a default.
A good use is review: read what you wrote, mark one fix, and stop when it rings. 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 17 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 17 minutes timer on a projector?
Press start, then F or the fullscreen button. Classroom mode hides the writing so the digits fill the wall. A good use is review: read what you wrote, mark one fix, and stop when it rings.
What is 17 minutes actually good for?
Seventeen minutes is long enough to get into a task and short enough that you can see the far side.
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.