Subject to subsection (b) of this section, a member is entitled to eligibility service for periods of employment while a member of the Local Fire and Police System. If a member completes at least 500 hours of employment while a member in any fiscal year, the member is entitled to 1 year of eligibility service. Except in the first and last fiscal years, a member may not receive any eligibility service for a fiscal year in which the member completes less than 500 hours of employment while a member. In the first and last fiscal years, if a member completes less than 500 hours of employment while a member, the Board of Trustees shall prorate the eligibility service based on the number of hours worked.