The Department may, at its discretion, make emergency inspections at other than normal working hours when requested to do so by the permittee. The Board, with the concurrence of the City Administrative Officer, shall determine from the cost of such inspection the fee therefor for every four hours, or fraction thereof, of inspection time pursuant to the provisions of Section 57.106.7. For the purpose of this section, normal working hours shall be construed to mean the hours between 8:00 a.m. and 5:00 p.m. of any day except Saturdays, Sundays, and legal holidays.