Where any special assessment is made under sections 31-501 to 31-523, the order making such assessment may provide that it be divided into equal annual installments, not more than twenty in number with interest at seven percent, payable on the whole amount unpaid annually with the installment that year falling due, and in such case the several installments of principal and interest shall be collected and payment enforced in the same manner as delinquent taxes, and sale of the land for a delinquent installment shall not be a discharge of the premises from installments subsequently to fall due; Provided, however, in case of special assessments, the owner of the premises may pay the entire assessment imposed at any time within ninety days after such special assessment is made.