The board may provide by rule and regulation for the retention of any legally qualified member who has temporarily ceased employment as a peace officer and for credit for such period, provided that an application for retention of membership is submitted not later than 90 days after such employment has ceased; and provided, further, that he shall pay to the fund the amounts required for such period. Not more than 12 months of absence from such employment shall be allowed under this Code section during a member's entire membership in the fund.