The standard workweek for employees occupying full-time positions consists of 40 hours unless otherwise specified by the Board of Supervisors. The appointing authority shall fix the hours of work with due regard for the convenience of the public and the laws of the State and County. Employees occupying part-time positions shall work such hours and schedules as the Board and the appointing authority shall prescribe. Except as hereinafter provided, County offices shall be open for business from 8:00 a.m. to 5:00 p.m. every day except Saturdays, Sundays and holidays. With the County Manager’s approval, department heads may make such changes to the schedule of office hours as public convenience or necessity may require.