since you are staying onsite is it possible to visit the parks the day of and day after you check-in? Even if onsite you really need at least two days to even to begin to experience the parks.
PS not 'some' attractions, most have the FOTL perk. The joy of staying onsite for most is the fact that you don't have to commando thru the parks, it's a nice leisurely experience.
Once you dig around here for advice, suggest you head to the universal website to do some hard-core planning. Look at the maps to get a feel for the layout then do some research on the various attractions to see what ones are a must-see for your family if you only have one day to visit the parks. There are various guidebooks out there that are very handy for a 1st time visit.
If you're into HP, by all means visit it 1st during your early entry & the water attractions in IOA last.
The parks are not open late like Disney...I didn't get that...but anyway....decide what you want to ride and plan your attack....with the FOTL perk for staying onsite...you should have no problems doing what you want.
We did each park a seperate day...but only spend half a day in each.
The studio side seems to have way more as far as simulator rides etc....but most of my party did not want to ride much.
Island...if you are doing harry potter...def head there first....such a busy place!