Yes, they do have express options for many of their attractions there. You can either pay for it directly, or if you stay at the upper end Universal hotels, you get it included for everyone staying in the room. During busier times, it's really nice to have. During slower times, it's not always that big an advantage. But since you're not sure exactly when you're going, that can be a tougher call. If you have the express option, 2 days is most definitely enough time.

We have stayed on site a few times, and loved the convenience of the hotels and the Express Queue. We really like Universal - Islands of Adventure is one of our favorite parks anywhere. You might already know this, but if you wish to take the Hogwarts Express between parks, you will need to purchase a hopper ticket. If you're not worried about that, you could easily purchase a 2-day, single parks type of ticket, and just do a single park each day. The only thing you miss is the train (and the flexibility of moving back and forth). With how close the 2 parks are, sometimes that hopper is a nice option! If you want to do things in a more relaxed fashion, 3 days would work, too!

Best of luck with your planning! Have a great trip!