Cal. Gov. Code § 32038

If any member is compelled to be absent from his employment because temporarily incapacitated for the performance of duty as the result of injury or disease occurring in and arising out of his employment, because of which he becomes entitled to workmen’s compensation, within 90 days after his return to active employment, or within 90 days after the effective date of this section, whichever first occurs, or within such further time as may be granted by the board, he may pay into the fund an amount equal to that which would have been deducted had he remained in active employment. Upon the making of such payment, such time, whether before or after the effective date of this section, shall be considered as time served as a county peace officer.