This parameter sets up the guard time for keeping volatile slots.
When a slot is declared as volatile (not reusable), it will be automatically deleted when a student changes is appointment assignation, feeing completely the slot, or when a teacher revokes all appointments on it. The deletion takes place when the slot starts too close to the actual date.
The parameter specifies the delay, from "now on", under which a freed slot will be deleted and will not be available for further appointments.