To 8thdwarf, you could see IOA in a day with a 1 day ticket. Just get there before the gate opens at 9am and you'll get on all the rides. Then the park fills up with 1 hour waits. An hour before closing you can get on all the rides again.
To mlm228, no way. You can't physically see both parks in 6 hours. The Express machines sell out by noon. They shut down with a message that says, "No Future Passes are Available for this attraction." So buying the 2 day pass does you no good. If you bought a 1 day ticket, and entered IOA around 02:30pm like you said, the wait times for the big attractions will be 1 hour. But as the sun goes down and the field trip busses leave, you can get a few rides. Even then, you won't see everything at IOA, it's physically impossible to do all the rides in a few hours on a Saturday. Get the 1 day ticket, enter the park, and go all the way to the back and ride Deuling Dragons. Then go on Jurassic Park and by that time the lines may be less at the big rides near the front of the park. But I doubt it. Was just there last week and Spider man had an hour wait at the close, Hulk was 30 minutes. Popeye was a walkon, but you get soaked. Doom Drop was also a walkon. You'll see the park and get a few rides this way, but don't expect much, place is packed.