You can take as long as you need but once you go through a room you can't go back. I spent 1.5 hours there just on my own.
It takes roughly 1-1.5 hours to go through all the rooms. And you can't go back, only forward. They don't rush you at all. You can take as much time as you'd like. You're not required to stay with the group you initially entered with, either.
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