The boards shall grant every member of the police force who has served for one year or more a total of three weeks vacation each year with pay, and each member of the police force who has served the department for twelve years or more shall receive four weeks vacation each year with pay, and each member of the police force who has served the department for twenty-one years or more shall receive five weeks vacation each year with pay, and each member of the police force who has served the department for thirty years or more and is eligible to participate in the deferred retirement option plan shall receive six weeks vacation each year with pay; however the board may grant an additional week of paid vacation to members after one year of service. All members of the police force shall receive fifteen holidays with pay, however the board may grant additional holidays with pay, and one hundred four days off duty each year with pay, and the boards may from time to time grant additional days off duty each year with pay when in the judgment of the boards, the granting thereof will not materially impair the efficiency of the department.