How do I disable alerting for a contact (temporarily)?

Planned in advance, e.g. for leave of absence

You can easily schedule employee leave in advance in the duty schedule by creating an additional (temporary) shift on top of the existing shift.

See 2.3 Two week schedules | weekly change call sequence | scheduled holidays for further explanation.

Unexpected, e.g. illness or absence due to calamity

You can easily set contacts to Absent in the Contacts menu.

See Contacts|Contacts set as absent for further explanation.