It's a challenge, but you can do MOST of both parks in a single day.
My attack plan strategy is simple. Start with IOA. Get there when it opens (which means, make sure you're pulling into the parking lot at least a half-hour before the actual open). As long as you're ahead of the crowd, you can lead the way going clockwise (starting with Marvel -- Spider-Man & Hulk) and be done with minimal lines for most of the attractions by noon or earlier.
Then you can head out to USF where the crowds will already be in place, but at least you have several more hours for it.
And I'm suggesting IOA first because the rides are typically shorter than USF. So most of that time is spent in queues if you show up later in the day, whereas it may be the other way around at USF where many of the attractions are longer, have pre shows, live elements, etc.