Sleep

Sleep is a command that sleeps for a certain amount of time. For millisecond sleeps, use usleep.

Sleep to the nearest minute or hour

This can be done with some bash arithmetic and applying modulus to 60 seconds for 1 minute or 3600 seconds for 1 hour.

# Next minute
sleep $((60 - `date +%s` % 60))

# Next hour
sleep $((3600 - `date +%s` % 3600))

With millisecond precision

If you need to synchronize a task by the millisecond, you can use date +%s%N which will print the timestamp with nanoseconds. Divide by 1000 for milliseconds and apply the same logic as above.

# Next minute
usleep $((60000 - (`date +%s%N` / 1000) % 60000 ))

# Next hour
usleep $((3600000 - (`date +%s%N` / 1000) % 3600000 ))

Synchronizing bash scripts with this method works quite well as long as all the machines are using the same NTP server. I was able to precisely synchronize an audio file playing across an entire computer lab of over 100 machines through the PC speaker back in 2017.