8 CFR 241.33: Expulsion.

(a) Execution of order. Except in the exercise of discretion by the district director, and for such reasons as are set forth in § 212.5(b) of this chapter, once an order of deportation becomes final, an alien shall be taken into custody and the order shall be executed. An order of deportation becomes final in accordance with 8 CFR 1241.31.

(b) Service of decision. In the case of an order entered by any of the authorities enumerated above, the order shall be executed no sooner than 72 hours after service of the decision, regardless of whether the alien is in Service custody, provided that such period may be waived on the knowing and voluntary request of the alien. Nothing in this paragraph shall be construed, however, to preclude assumption of custody by the Service at the time of issuance of the final order.