21 U.S. Code § 879 - Search warrants
A search warrant relating to offenses involving controlled substances may be served at any time of the day or night if the judge or United States magistrate judge issuing the warrant is satisfied that there is probable cause to believe that grounds exist for the warrant and for its service at such time.
1974—Pub. L. 93–481 struck out designation “(a)” before “A search warrant”, and struck out subsec. (b) which permitted officers authorized to execute search warrants to break open and enter premises under certain circumstances and which required that such officers identify themselves and give reasons and authority for their entry after such entry.