My friend and I were at the parks a little over a month ago, and we got to universal studios around 1130am. We went on the Mummy first, just because it was early and I wanted to ride something less intense to start out with in the morning. Mummy took about 20 minutes to get on, and then we headed to Rip Ride Rockit. We waited in that line for about 50 minutes. I would assume the line will be a pretty decent wait, as it IS a somewhat newer ride. I'd probaby hit that ride up pretty early to avoid long waits.
One thing that I DID NOT like about the ride, is how it goes straight up when it begins to take you to the first drop. I didn't pull my harnest tight enough and i could feel myself slipping out of the seat as my iphone also was slipping out of my pocket. It was not a very comfortable start to the ride. However, after we got to the top of the drop, the ride was amazing. Kinda stinks that it only goes upside down one time though. Had they thrown in 2 or 3 more parts where you are upside down, it could be one of my favorites.