Any member accruing annual leave or sick leave days may, after April 9, 2005, elect to use the days at the time of retirement to acquire additional credited service in this retirement system. The days shall be applied on the basis of two workdays' credit granted for each one day of accrued annual or sick leave days, with each month of retirement service credit to equal twenty workdays and with any remainder of ten workdays or more to constitute a full month of additional credit and any remainder of less than ten workdays to be dropped and not used, notwithstanding any provisions of the code to the contrary: Provided, That for a person who first becomes a member of the retirement system on or after July 1, 2015, accrued annual and sick leave days may not be applied to acquire additional credited service. The credited service shall be allowed and not considered to controvert the requirement of no more than twelve months' credited service in any year's period.