The following members who are employed by the day or by the hour shall have 175 days or 1,050 hours as the basis for determining their earnable compensation for a school year:

Full-time day service, or full-time service as performed by members whose normal tours of duty extend throughout the school term (hereby defined for purposes of this retirement system as being the period beginning with the day upon which school commences and ending with the day upon which school closes in the same year) shall be performance of assigned duties for six hours per day for five days per week, or the equivalent thereof. Performance of assigned duty for a shorter period than six hours for five days per week, or the equivalent thereof, such as but not limited to performance of duties for four hours per day for five days per week, but for which such member receives compensation in the same amount as he would have received if such performance were six hours per day for five days per week, shall nevertheless be counted as a full-time day or full-time service.