Persons against whom the assessments have been made may pay such assessments in equal installments over a period of eight (8) years or if provided for within the specific assessment ordinance, up to 18 years. Such assessments may be paid in equal annual installments; provided, however, that one-runth (1/9) of the assessment on an 8 year payment period, or the equivalent pro rata share if a longer installment period is provided, shall be paid on or before the due date, and the balance shall be paid in equal, proportional, annual installments thereafter together with interest on the unpaid balances at an annual interest rate, as set in the assessment ordinance, not to exceed the rate of one-year United States Treasury Bills at the time the assessment ordinance is adopted, which rate shall be determined by the Director of Finance.  Such installments shall become due at the same time that real estate taxes become due and payable in the Town, and the amount of each installment, including principal and interest, shall be shown on a bill mailed not later than fourteen days prior to the installment due date to each such person by the treasurer or his designee.  If any annual installment is not paid within thirty (30) days after the due date, then the entire unpaid balance shall be declared due and payable and collected in any manner permitted by law.