Ok, since you are not staying onsite, you have the option to purchase the express pass at the gate. The passes for either day will cost $31.99 per person and will give you express access to every ride in the park (except the main HP one, a kid one in Jurrasic Park, and the Rip Ride Rockit) and will let you use the express line once per ride. It really depends on the crowds and how many rides you want to see. When we stay on-site, we are able to do both parks in one day riding just about every ride in both parks because of express...but we have to move it. You can't really stand around or go explore the parks. You just have to move from ride to ride. Keep checking the trip reports and looking at the wait time for rides (there is a site someplace that has the current wait times. Check it on sunday and monday to see what day seems to have shorter waits). If the waits seem to long, express will be your only option since Universal does not have a Fastpass system.