Manufacturing establishments may be granted a special license by the labor commissioner excepting them from N.H. Rev. Stat. § 276-A:11 and 12 for not over 8 weeks in any 6-month period, but in no case shall the hours of labor exceed 10-
1/4 hours in any one day or 54 hours in any one week. Before granting such license, a hearing shall be held by the commissioner and he shall be satisfied that such overtime is necessary. A copy of such license shall be posted in a conspicuous place in every room where youths are employed.