All bid guaranties, except those of the three lowest bona fide bidders, shall be returned immediately after bids have been checked, tabulated, and the relation of the bids established. The bid guaranties of the three lowest bidders shall be returned as soon as the contract bonds and the contract of the successful bidder have been properly executed and approved. When the award is deferred for a period of time longer than 15 days after the opening of the bids, all bid guaranties, except those of the potentially successful bidders, shall be returned. If no award is made within 30 days after the opening of the bids, or such other time as specified in the bid documents, all bids shall be rejected and all guaranties returned, except for any potentially successful bidder that agrees in writing to a stipulated extension in time for consideration of its bid, in which case the awarding authority may permit the potentially successful bidder to substitute a satisfactory bidder’s bond for the cashier’s check submitted with its bid as a bid guaranty.