These are the conventional limits rather than rules. What matters is that the number is chosen before the meeting and visible during it.
Agree the length before it starts, put it on screen, and let the beep end the item rather than someone having to interrupt. Press the slot you agreed in the table below and it is running before the meeting starts.
Yes. Share the browser tab in your video call and the digits are visible to the whole room. Zoom in with the browser's own zoom so the numbers are readable at the back of a meeting room.
Start a fresh countdown rather than removing the limit. That keeps the overrun visible and deliberate, instead of a timebox that quietly dissolved — the point of the timer is not the number, it is that everyone agreed to one.
Yes. No account, no install, and nothing to license. It runs in the browser, which also means it works on a meeting-room computer you have never logged into before.