Definitely doable in a day! We were there last year at the exact same time and the lines were not bad at all. We got there right at park opening and had plenty of time to do our favorites and then some of them a 2nd time. I can't remember if Back to the Future is closed yet, but honestly it was a waste of time for us, not a very comfortable ride. I can understand why it is being closed. We went during the week and did one day at USF and then went back and did a day at IOA, with grandparents & 2 little ones in tow I might add. After the grandparents left, we went back again on a Saturday and hit all our favorites at both parks. The parks were much more crowded on Saturday and there seemed to be a lot of church and school field trips.
If you go to USF first, do Mummy first. If you go to IOA, do Hulk first. One morning we were able to ride Hulk a couple times because there were no lines before we headed on to the rest of the park.
I did see some people with the Express Passes, but they didn't really need to use them. They would enter the ride at the same time we would just through a different line and then they would be loaded before us, but then we were right behind them, on the same ride.
Get there early and during the week and you will have plenty of time!