How to refer to different "sleep time" of multiple people? [closed]

The lengths of time periods are different. Should I use "..., whose sleep times are different"? Or just "..., whose sleep time are different"?

Solution 1:

Sleep times if you mean many individual people and want to indicate their individual sleep times are different.

We don't want the heater to have fixed start and stop times, because people's sleep times are different.

Sleep time in the special case of the people being in a different time zone (from the reader) and having a common problem of being different, rather than their individual sleep times being different from each other.

It was less convenient for British listeners to benefit from the live internet broadcast of the soothing night-time sounds from the Indonesian forest, because their sleep time was some 7 hours different from that of local Indonesians.