(a) Time Off With Pay. Whenever a member, for overtime work, shall take a period of time off with pay:
(1) a deduction for pension purposes shall be made from such pay but only in the same amount as that which would have been deducted from his regular salary if such period had been one of regular work;
(2) such pay shall be part of the salary assigned or attached to the rank or position held by him but only in the same amount as that which would have been his regular salary if such period had been one of regular work; and
(3) such period shall be part of his years of aggregate service.
(b) Cash Payment. Whenever a member, for overtime work, shall receive a cash payment:
(1) a deduction for pension purposes shall not be made from such payment;
(2) such payment shall not be part of the salary assigned or attached to the rank or position held by him; and
(3) the period of overtime work for which he shall receive such payment shall not be part of his years of aggregate service except that any period of a member’s overtime work, for which he shall not have taken time off with pay, shall be credited, by the Board, as part of his years of aggregate service, upon his or his survivor’s written request therefor, to the same extent as he would have been entitled to take therefor time off with pay but only to the extent, and not in excess thereof, that he, while a member, shall have had any period of absence from work without pay. Such request shall be accompanied with payment of the amount which would have been deducted for pension purposes from his regular salary if the period of overtime work, to the extent credited, had been one of regular work.