N.H. Rev. Stat. Ann. § 41:2-i

If a town votes to adopt the provisions of this subdivision, the change shall not take effect until the first annual town meeting following the meeting upon which the questions were acted upon. At the next annual meeting following the meeting where action was taken, the town shall elect one member for a one-year term, one member for a 2-year term and one member for a 3-year term. At each succeeding annual meeting, members shall be elected to fill the vacancies regularly occurring.