By default an event is visible immediately upon its approval for publication to a target audience and is removed from visibility when its end date & time elapses.
Event suggestors can not only suggest an event, but suggest the period of time during which an event should be visible. Event approvers can override a suggestor's publication period or establish a custom publication period for an event. A publication period is defined by a start date & time as well as an end date & time on a per target audience basis.