For minutes, the minimum is 15 minutes, and in increments of 5 minutes up to the maximum of 150 minutes.
For hours, the minimum is 1 hour, and the maximum is 23 hours.
For days, the minimum is 1 day, and the maximum is 28 days.
Also, for booking by minutes & hours, overnight booking is not allowed. For example, a booking from 11 AM -1 AM next day will not be possible.
You can find more information on custom units and how services are listed on your marketplaces here.
Otherwise, if you are looking to implement other custom units of time, you can find more information on adding your own custom codes here.