Sorry for being so MIA on this thread! But to answer the question about it lasting 50 minutes...YES its definitely possible. I've used it as a full lesson. Usually I can make it last the entire time by:
-When explaining the five different kinds of yes/no questions, call on individual students and ask them a question using that form to reinforce the idea. Also, if you do silly ones then a tangential conversation comes out of it, but they're still using English so I don't mind the tangents so much!
If you're brave, you can turn the tables around and tell them that they can ask you any question that has a yes/no answer. This gets them speaking/asking questions but it might invade your privacy though, haha.
With lower level students tell them that they have to pick an item in the classroom so that usually makes the guessing a lot easier and the game go quicker. For my higher level students I did something abstract or really difficult like "The Pyramids of Egypt" (which they actually guessed!) or "Pi" They get a real kick out of it though. Hope that helps!