N.H. Rev. Stat. Ann. § 669:45

The time the polls shall be open at caucuses shall be fixed by the executive committee of the party in the town holding the caucus. In towns and wards having not more than 2,000 inhabitants, according to the last preceding national census, the polls shall be open not less than 2 hours, and, in those having more than 2,000 inhabitants according to such census, not less than 3 hours.