(1) When the assessment of benefits has been made and filed, as provided herein, the property owner shall have the right to pay such assessment of benefits in full within sixty (60) days thereafter, but, if he does not avail himself of this privilege, the assessment of benefits shall bear interest at the rate of six percent (6%) per annum.
(2) The interest need not be computed until necessary to be sure the collections have not exceeded the total amount of the benefits so levied.