Police/investigators don't "schedule" take downs in the same sense that a programmer/manager would schedule a project launch. The FBI wouldn't plan to make the takedown they factor it around multiple situations and a big one is that of future "threat". The police gather evidence long enough until they have an open/shut case against the convicted but should intelligence arise that the suspect is planning a major move that puts people in danger they'll act on what they have and try to make it work in the sense that they'll be protecting others.

I'm just playing devil's advocate here, but actions by the Mega staff may have triggered such a reaction. Its not unheard of for something "in the works" to trigger the takedown.