If you are staying on property at Universal they offer early entrance to a park one hour early. You are funneled back thru the park to HP area. There you are free to ride the rides before park opening. Do that area then ride the train over to the other park. Depending which park is open early you will need to adjust your park touring accordingly. I would work my way forward thru the park to the front. If you are staying multiple days, then go back to the park that you initially went thru and see those attractions you missed the day before.