Just got back from there a few weeks ago and if you only have an 8 to 9 hour window you won't have time to do everything in both parks. We spent 2 half days each in just the harry potter areas and that included our early entry from staying on resort and without that you'll wait 2-3 hours for the new Gringotts ride. The older harry potter ride is better though and you'll have like a 30-45 minute wait. Plus the express pass mentioned above ^^^^ DOES NOT work on the harry potter rides. So if you want any chance of getting it all done in one day go to the older harry potter land first run through all the Island of Adventure rides then hop over to Universal Studios itself do all of their rides and then end with gringotts at the end of the day....and an Express Pass is a MUST for all the non-harry potter stuff if you want to get all done in one day!!!