Any full-time employee of a city recreation commission who is eligible for receipt of a pension pursuant to this chapter may, with the approval of, and under terms and conditions set by, the board of trustees, have that person‘s previous full-time employment with the city recreation commission of that city counted as a portion of the two hundred forty months of service required by section 40-46-09. The credit given for previous service with the city recreation commission pursuant to this section shall not exceed one hundred twenty months in total. Board of trustee terms shall include payment of pension fund contributions by the employee for the months of service credited.