Every person employed by the district in a position requiring certification qualifications in a day school of the district for not less than the minimum schoolday for each day the schools of the district are maintained during the school year is a full-time employee and his compensation shall be fixed accordingly. Governing boards may require persons employed in positions requiring certification qualifications to serve a longer period time in each schoolday than the minimums defined in Sections 46112 to 46116, inclusive, and 46141, in order to be compensated as full-time employees, provided all such employees in similar grades or levels are similarly required to serve such longer periods of time, and provided that the duties required of such persons during such extended time shall be directly related to and restricted to their normal assignment. With respect to a unified school district, for the purposes of this section all day kindergarten and elementary schools of the unified school district shall be deemed to be maintained by one district and all day high schools of the unified school district shall be deemed to be maintained by a second and separate district.