In the past when I researched this it was theorized by some they used cables to "pull" it down, so that wouldn't take nearly as long. There's a demolition expert on YouTube who IIRC claimed something like this could be done and wired with explosives in a day or less, and in my own personal opinion I'm openminded that it could have been prewired for various reasons since it was such a sensitive building, however what the truth is I dunno.