The departments of the state government except where seven day per week services are maintained, shall remain open from nine A.M. until five P.M. from Monday through Friday, both inclusive, except on holidays fixed by law. On Saturdays such departments may close at one P.M. Skeleton forces may be maintained on Saturday and so staggered that each employee shall work not less than one Saturday out of each month; provided, that the offices of the Department of Motor Vehicles shall remain open from eight-thirty A.M. until five P.M. from Monday through Friday, both inclusive, except on holidays fixed by law and these offices need not be kept open on Saturdays, except as may be necessary to carry on essential work.