It may take several minutes. Wait and be ready to dial your number when you hear the dialtone. This will eliminate your need to make the call. It may take several days before the increased calling subsides. If aftershocks occur, do not use the phone unless you have an emergency.
Every aftershock creates a resurgence of use on the phone network, causing additional congestion.
The best time to place a call is between 10 PM and 6 AM when other calling has subsided.