I went to one in 2001. I met up with @Ringo and @thinksnow.
Yea, was there just last week. It helps that my office is only a half a mile away, though. 
I love the cold war hangar and the (new) missile exhibit in the very back. The Air Force One planes are cool. And their XB-70 Valkyrie is a sight to behold.
I think you can get a tour guide. But most people don’t, and I personally wouldn’t bother. With only three hours, I would just roam around. Would also not recommend a movie, as it will just eat into those hours.
PM me. If I can swing it I’ll meet you there.