The finding of the Department of Labor ascertaining and declaring the general prevailing rate of hourly wages shall be final for all purposes of the contract for public work then being considered, unless reviewed under the provisions of this Act. Nothing in this Act, however, shall be construed to prohibit the payment to any laborer, worker or mechanic employed on any public work, as aforesaid, of more than the prevailing rate of wages; provided further that nothing in this Act shall be construed to limit the hours of work which may be performed by any person in any particular period of time.