Three minutes is the longest of the everyday pacing beats — a spacious interval for tasks that genuinely need a few minutes each: a long stage in a process, a slow rotation, or a cue to step back and reset on a fixed schedule. One clear beep marks each window so nothing has to be watched.
It is the spacious end of the range, the beat for work a shorter interval would interrupt. Set a few rounds for a quick run or many for a long one, and it keeps the three-minute beat throughout.