Although the distance is not all that far (7-8 miles?) it may take awhile to get there, especially if you are going in the morning when you will be in the 'Orlando' bound traffic until you exit I-4.
I'm a conservative character so I'll say that from walking out the door of your Disney resort to walking in the gate at Universal Studios would easily take 35 minutes.
It takes a handful of minutes to go to the car and leave the resort, another handful to leave WDW property, maybe 10 minutes to go up I-4 to the Universal Exit, a handful of minutes to get onto Universal property and pay for parking, then at Universal you will park in a huge parking garage and will have to walk from there, through Citywalk to the parks, so say another 10 minutes.
Also - typically the parks will actually open their gates 15-20 minutes before the posted time so if you want to get there when it really opens you might want to leave an hour before posted opening time.
And nowadays Universal Studios and Islands of Adventure are offering early entry (1 hour earlier) on some days for people who are staying in their onsite resorts.
Sheesh, it's complicated!
Have Fun!
-bruce
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