38 C.F.R. § 3.378
A permanent and total disability rating in effect during hospitalization will not be discontinued before hospital discharge on the basis of a change in classification from active. At hospital discharge, the permanent and total rating will be discontinued unless (a) the medical evidence does not support a finding of complete arrest (§ 3.375 ), or (b) where complete arrest is shown but the medical authorities recommend that employment not be resumed or be resumed only for short hours (not more than 4 hours a day for a 5-day week). If either of the two aforementioned conditions is met, discontinuance will be deferred pending examination in 6 months. Although complete arrest may be established upon that examination, the permanent and total rating may be extended for a further period of 6 months provided the veteran's employment is limited to short hours as recommended by the medical authorities (not more than 4 hours a day for a 5-day week). Similar extensions may be granted under the same conditions at the end of 12 and 18 months periods. At the expiration of 24 months after hospitalization, the case will be considered under § 3.321(b) if continued short hours of employment is recommended or if other evidence warrants submission.
38 C.F.R. §3.378