48 C.F.R. § 871.207
(a) Contracts, agreements, or arrangements requiring the payment of tuition or fees must provide either of the following:
(2) An institution may be paid in accordance with paragraph (b) of this section, if the institution operates on a regular term, quarter, or semester basis and normally accepts students only at the beginning of the term, quarter, or semester and if the institution is one of the following:
(d) The period for which payment of charges may be made is the period of actual enrollment and is subject to the following: