For purposes of this Section, any driver who is gainfully employed in any other occupation for eight (8) hours or more a day shall be deemed a part-time driver. In no event shall a part-time driver operate a taxicab for more than eight (8) hours in any consecutive 24-hour period. No full-time driver shall operate, nor shall certificate holders or their agents require full-time drivers to operate, a taxicab for more than twelve (12) hours in any consecutive twenty-four (24) hour period.