What if your materials need to be released no earlier than midnight?.
The quarterly earnings statement, the grand prize winner, the press kit for the much anticipated film, the merger news?
Well, you send out the materials to the press with the "Do-not-release-before-such-and-such-time" statement and hope for the best.
Now the information can be made available at midnight or any time you specify, with all related materials such as photographs, bios, etc. released at exactly the same time.
Imagine the anticipation of "All materials will be made available on our Web site at 12:01 AM."
The scoop goes to those who wait for the information to be posted, not the one who releases your information early.