Head to your employee's profile > Work Time tab :
Click on 'Edit'
Select whether the employee is "available", "unavailable" or "partially available" and, in which case, you can specify the hours of availability
Save
Unavailability and partial availabilities are then displayed on the schedule, weekly !
Good to know :
In the scheduling part of your employee's profile, you will easily see their availability: in green (available all day), in orange (available part of the day), in red (unavailable).
If the employee's contract has not yet started, you’ll need to click on the Future Contract and then the "Schedule" tab to indicate their availability.
Indicating your employee's fixed availabilities is mandatory for part-timers !