I was there a couple of weeks ago, and saw just about everything in less than 3 hours.
The longest lines are for the simulator and the observation tower. There is also an IMAX theater, which would require more time...both standing in line and for the movie itself.
The exhibits don't allow for up-close observation. You can see the planes, but you can't kick the tires, look in the gear wells, go on-board, etc. The Shuttle Enterprise is there, but you have to observe at a distance.
There are also exhibits of engines, machine guns, uniforms, etc. There is also a Subway sandwich shop there, but prices are way too high (shocking!). And it costs $12 to park.
I think you should be able to see most everything in 5 hours. It depends on what your objectives are and how crowded it is. My recommendation is that you set priorities for what you want to see and visit exhibits in that order. Another option is to come back some day, as I plan to do.
Hope you enjoy your trip.
Flying Colors Forever!