N.H. Rev. Stat. Ann. § 149-I:16

The mayor and aldermen of any city may, in their discretion, in making any assessment under this chapter, assess the same to be paid in annual installments extending over a period not exceeding 20 years, and in such case their assessment so made shall create a lien upon the land on account of which it is made and the lien of each installment so assessed shall continue for one year from October 1 of the year such installment becomes due.