If some resources don't work full-time for the company, you may want to enter the agreed part-time schedule in the User edit panel. 

To do so, go to the User section, select the user and choose the tab Schedule

Note that the lunch break hours will also be represented so to automatically position the schedule accordingly.

The planner board will correspondingly show this number of hours on the specific days and as well grey out the slot this person is not available. 

 

Alternatively, this setting can be performed by the concerned user in his/her own User's profile. To do so, click on the User's Name  (top right corner) and then select Profile.

Every user can as well edit his/her daily parameters in the Schedule section of the profile menu: 

 

 

Last, especially for resources having irregular working times, you may simply book their unavailability by booking these slots as time-off and/or on a dedicated non-billable project (named for eg. "Not available").

If applicable, you can also make use of recurring bookings (say "every month").