(a) Except to the extent a court orders otherwise, a sentence of death shall be executed:

(1) On a date and at a time designated by the Director of the Federal Bureau of Prisons, which date shall be no sooner than 60 days from the entry of the judgment of death. If the date designated for execution passes by reason of a stay of execution, then a new date shall be designated promptly by the Director of the Federal Bureau of Prisons when the stay is lifted;

(2) At a federal penal or correctional institution designated by the Director of the Federal Bureau of Prisons;

(3) By a United States Marshal designated by the Director of the United States Marshals Service, assisted by additional personnel selected by the Marshal and the Warden of the designated institution and acting at the direction of the Marshal; and

(4) By intravenous injection of a lethal substance or substances in a quantity sufficient to cause death, such substance or substances to be determined by the Director of the Federal Bureau of Prisons and to be administered by qualified personnel selected by the Warden and acting at the direction of the Marshal.

(b) Unless the President interposes, the United States Marshal shall not stay execution of the sentence on the basis that the prisoner has filed a petition for executive clemency.