(a) Execution of order. Except in the exercise of discretion by the district director, and for such reasons as are set forth in § 1212.5(b) of this chapter, once an order of deportation becomes final, an alien shall be taken into custody and the order shall be executed. For the purposes of this part, an order of deportation is final and subject to execution upon the date when any of the following occurs:

(1) A grant of voluntary departure expires;

(2) An immigration judge enters an order of deportation without granting voluntary departure or other relief, and the alien respondent waives his or her right to appeal;

(3) The Board of Immigration Appeals enters an order of deportation on appeal, without granting voluntary departure or other relief; or

(4) A Federal district or appellate court affirms an administrative order of deportation in a petition for review or habeas corpus action.

(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.