Hi Tink!
I just returned from a day (+2 hours the next morning) at DLP and we were able to see everything we wanted in both parks and not feel rushed. However, this was in early April not the summer so I'm not entirely sure how the crowd situtation will be when you are there. Like someone above said, if it's too crowded, don't even bother with Studios. There's really not too much to do there and it's not terribly exciting, but worth it if you have time (and more relaxing due to less crowds). Anyhow, the "must sees" I would say are Indiana Jones and the Temple of Peril (awesome) and Space Mountain 2. Don't know what kind of rides you're most interested in, but we tried to do everything that was different from WDW - including little kid rides like Casey Jr., the Storybook Cruise, Pinocchio, the little Aladdin walkthrough area, etc. And obviously, if you love BTMRR and Haunted Mansion (Phantom Manor) and PoC, go on those too. But it's definitely doable in 1 day if you're there early enough. At Studios, I thought RnRC was way better than the Florida one so that's worth checking out if you like that kind of thing. I also enjoyed the Cinemagique show. Hope this helped!