This page opens with the timer already set to 3 minutes. Press Start or hit the spacebar and it begins; when time is up the alarm rings and the disk blinks. You can always drag the disk to a different time.
For short bursts, a shape beats digits. A 3-minute disk tells you what's left in one glance, so you keep moving instead of checking a clock.
The 3 minute timer classic is steeping tea — it also fits one breathing exercise or a stretch set.