Fifty-nine minutes leaves a single minute to be standing at the door when the next thing starts. Start the clock when the real work starts, not during announcements.
If someone asks to round it up, the extra minute was the one you needed for the hallway. 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 59 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 59 minutes timer on a projector?
Press start, then F or the fullscreen button. Classroom mode hides the writing so the digits fill the wall. If someone asks to round it up, the extra minute was the one you needed for the hallway.
What is 59 minutes actually good for?
Fifty-nine minutes leaves a single minute to be standing at the door when the next thing starts.
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.