The board of trustees shall fix and determine by proper rules and regulations how much service in any year is equivalent to one year of creditable service, but in no case shall more than one year of service be creditable for all service in one calendar year, nor shall the board of trustees allow credit as service for any period of more than one pay period’s duration, as shown on the salary and wage schedules of the employer, during all of which the member was absent without pay unless such member pays the employee contributions, including contributions by the employer in lieu of employee contributions, for such period as permitted by the board of trustees in accordance with the provisions of section 169.315.