The Fund will be liable for the payment of interest if payment has not been made within 30 calendar days after the receipt of a proper invoice for the amount of the contract payment due, except when the contract payment is subject to the conditions set forth in section 1003.5 of this Part. Any time taken to satisfy any of the conditions set forth in section 1003.5 of this Part will extend by an equal period of time the date by which contract payment must be made in order for the Fund to be liable for interest payments.