38 C.F.R. § 21.344
(a) Approval of leaves of absence required. Leaves of absence normally must be approved in advance by the case manager when the facility offering training or rehabilitation services arranges for the leave. The approval of the case manager is required:
(c) Conditions permitting approval of leaves of absence.
(2) An additional period of up to 15 days of leave in the same twelve-month period under exceptional circumstances may be approved by the case manager if failure to approve leave will:
(ii) Adversely affect the veteran's ability to continue in his or her rehabilitation program.
(Authority: 38 U.S.C. 3110)
[49 FR 40814, Oct. 18, 1984, as amended by 56 FR 14649, Apr. 11, 1991]