That phrase has a contractual meaning.
It's most often used in real estate when one submits a contract and establishes the time for response. Once set, the clock begins once the other party receives it.
Guess that depends on who's in charge of those police.
I was thinking maybe the tweet was announcing a hit BEFORE he was taken into custody. But it's just as plausible that the police are on the take. Maybe it will depend on what happens to him sooner rather than later. See time is always of the essence.