There is a scene in that recent shogun series where a team performs a raid.

The leader sends the team in in small waves and “times” each groups entrance by counting rhythmic taps on his shoulder.

I thought it was such a great detail to include.

Of course rhythm would be the measure of time without a watch to look at.

One of the medieval time measurements were standard prayers - a Pater Noster is about the same amount of time each time, and a decade of a rosary for a given person will be pretty consistent.

Two more modern anecdotes of using songs for rhythm or timing:

The ideal pace for CPR chest compressions is pretty much exactly Stayin' Alive by Bee Gees. Or if you like darker humor, Another One Bites the Dust by Queen.

At the peak of COVID-19, the recommended duration for hand washing was Happy Birthday twice.

Reminds me of how the Pueblo leader Popé distributed ropes with knots tied in them to various groups across the region to coordinate his attack. Every day each group would untie one knot in their rope, and when all the knots were untied they were to attack the Spanish.