Since version 5.12.2 we have access to the Mercury API item that controls overrides. This is awesome for 2 reasons:

Configuring an Override

Please note, converting time zones no longer applies. Enter time normally.

Determine which doors need the override - generally only exterior doors will ever need to be altered; use your best judgement
NEVER set an override on an alarm
Navigate to Physical Access
Use the checkboxes on the left to select the desired doors.
Click the override button.
Once inside the override box give the override a name, select the desired door mode, partition (your school), and select starting/ending time.

Please make sure to select a partition. If not selected all users in the access control manager (including ones from other schools) will be able to modify your override!

Editing an Existing Override

Once an override is created it can be edited.