No woman shall be required or allowed to work in any factory except between the hours of 6 A.M. and 7 P.M.; provided that the State Government may, by notification in the Official Gazette, in respect of any factory or group or class or description of factories, vary the limits laid down in clause (b). However, no such variation shall authorize the employment of any woman between the hours of 10 P.M. and 5 A.M.