(1) Where the State Government is satisfied that, owing to the nature of the work carried on or to other circumstances, it is unreasonable to require that the periods of work of any adult workers in any factory or class or description of factories should be fixed beforehand, it may, by written order, relax or modify the provisions of section 61 in respect of such workers therein, to such extent and in such manner as it may think fit, and subject to such conditions as it may deem expedient to ensure control over periods of work.