N.H. Rev. Stat. Ann. § 600-A:3

The regular term of the multicounty grand jury shall be 6 months. The terms may be shortened by the supervising judge at the request of the attorney general. The term may be extended by the supervising judge for a specified time period upon a written petition by the attorney general stating that an extension is needed to conclude a multicounty grand jury begun prior to the expiration of its term.