How does overtime work?
Go to Control Panel in the side menu and click the Enable overtime checkbox.
Enter the amount of overtime in seconds. Add 60 seconds and if a bid is placed in the last 60 seconds of the auction the auction will be extended by a further 60 seconds. If no more bids are placed during the overtime the auction will close. If a bid is placed during the overtime an additional 60 seconds will be extended by a further 60 seconds. This will continue until no bids are placed.