how long does it take to beat?
There are essentially 12 "endings," and you could beat any of them in under 10 minutes if you knew the exact course of events. Buuut part of the fun is not being sure of how to progress and messing with things to find your next clue.
I got all twelve endings in three to five hours, and I got them all in two sittings. The only thing that slowed me down too much was that one mission glitched out on me.