It’s not really a full day attraction. I couldn’t imagine spending more than 4-6 hours there… and I think 6 is really pushing it.
If you go late at night (I think within two hours of closing) there is a special where it is half price entry. It’s less crowded at night, and there is hardly a wait for anything. You could easily do everything there in the last two hours it is open, especially on a week night (we were there Saturday night, Saint Patrick’s Day… it was absolutely packed in DtD but there were hardly any people in Disney Quest).
It’s pretty fun. My favorite games were Pirates of the Caribbean, which is like Toy Story Mania with the same type of cannon, except you’re in your own little room that moves and you shoot ghost ships and sea creatures. I also liked the Jungle Cruise, which is a raft ride simulator, Cyber Space Mountain (a very popular design-your-own-rollercoaster simulator) and Buzz Lightyear Astro Blasters. My boyfriend and I had a good time, and we are in our early 20s, so I’m sure your 12 year old would have a blast, especially if he enjoys video games.