Prior to the delinquency of a fee due under section 3.650, the city manager or designee may, for good cause, extend the time for filing an occupancy fee return and making payment of the fee due thereunder, for a specific period of time not to exceed 30 days. A person to whom such an extension is granted shall pay interest at the rate of one and one-half percent per month on the amount of fee due, without proration for a fraction of a month. If the report is not filed, or the fee and interest due is not paid by the end of the extended time, the interest shall become a part of the fee for computation of any penalty under section 3.665.