The council may provide for the payment of special assessments in annual installments, not to exceed thirty in number, the first installment being due upon confirmation of the roll and the deferred installments being due annually thereafter or, in the discretion of the council, may be spread upon and made a part of each annual city tax roll thereafter until all are paid. Interest may be charged upon deferred installments at a rate not to exceed the maximum allowed by state law. Under any installment plan adopted, the whole or any deferred installments with accrued interest to date of payment may be paid in advance of the due dates established.