Payments of interest and principal shall be made to the State Treasurer. A loan from the Literary Fund shall be repayable in annual installments from five to thirty years. The time of payment may be extended in the discretion of the Board of Education; but if the Board of Education has assigned any of the bonds, notes or other evidences of the loan to the Board of Trustees of the Virginia Retirement System under the provisions of § 51.1-124.30 and the same are held by the Board of Trustees of the Virginia Retirement System, the time of payment thereof may not be extended by the Board of Education but may be extended by the Board of Trustees of the Virginia Retirement System, in its discretion.