Ouch!! Not much time. I agree with the consensus that the Cairo museum should be top of your list.
You could go to the visitor center, see the museum there and the short film, then drive straight through the park to Cairo. Those two places WITHOUT stopping in between will just about be 2 hours worth. On your way out of park, you could stop by Stockade Redan and take some pictures there.
With that time limit, those are the 3 places I suggest. You might could squeeze 2 hours out with those and not regret missing too much.
Anyway, my thoughts..... have fun and share your pictures with us!!