§1. Delegated power ceases: by fulfillment of the mandate; by expiration of the time or completion of the number of cases for which it was granted; by cessation of the purpose for the delegation; by revocation of the one delegating directly communicated to the delegate as well as by resignation of the delegate made known to and accepted by the one delegating. It does not cease, however, when the authority of the one delegating expires unless this appears in attached clauses.
§2. Nevertheless, an act of delegated power which is exercised for the internal forum alone and is placed inadvertently after the lapse of the time limit of the grant is valid.
Source: Code of Canon Law (Vatican.va)