If the school board of any district shall decide that, by reason of special conditions or circumstances, the maintenance of standard schools for 180 days, or the equivalent number of hours if approved by the commissioner of the department of education, in said district is undesirable, said school board may so represent in writing to the state board. If, upon hearing, the state board, or the commissioner when authorized by the state board, shall be of the opinion that the representation is true, it may reduce the time of maintaining such schools in said district to such limits as it may deem wise. Provided, however, that the state board, or the commissioner if authorized, shall not reduce the days during which schools shall be in session, as provided in N.H. Rev. Stat. § 189:1, on account of workshops, conventions or teachers’ institutes.