The rate of extra compensation for Sunday or holiday services is hereby fixed at twice the gross daily rate of regular pay of the employee who performs the service, for any and all services totaling an aggregate of not more than nine hours, with one hour for food and rest, during the 24 hours from midnight to midnight of the Sunday or holiday including actual waiting time and time required for travel between posts of duty but not including other time not spent at the post of duty. This rate shall apply regardless of the length of time served within the aggregate of the aforesaid 9 hours, whether it is served continuously or in broken periods, and whether it is served for one or more applicants. Services in excess of an aggregate of the aforesaid 9 hours performed during the 24 hours of a Sunday or holiday shall be compensated on the same basis as overtime services performed at night on a weekday, the time between the completion of the aggregate of the aforesaid 9 hours and midnight being considered as the hours of a night. The maximum amount which may be paid an employee for services performed during the 24 hours of a Sunday or holiday shall not exceed four and one-half times the gross daily rate of his regular pay.