Managing your staff/trainer's schedule, balancing shift patterns and ensuring that appointments logged are within working hours can be done through the Roster feature...

To set this up, head over to your Trainers settings area, then down to the Roster section:

By selecting one of the slots, you can then edit the hours accordingly. You can also setup multiple split schedules throughout the day.

Once you've setup the roster's schedule, it is reflected in other areas within PTminder:

On the Trainer's Calendar, the unavailable times will be blocked out:

You'll receive warnings when attempting to book in sessions/classes inside an unavailable time-frame:

And finally, if you have online session bookings enabled for your clients, they will not be able to request bookings outside of those rostered timeslots.