There are 3 acts in the main game, and act 4 is a Halloween DLC. Since the main game is just one night, each act is 2 in-game hours.

Act 1: Hour 1 & 2,

Act2: Hour 3 & 4,

Act 3: Hour 5 & 6.

And of course, minigames after each act.

And don't worry, you won't be sitting in one single office for all 3 acts)