Hi! I am still thinking about a possible June trip. We would be staying onsite, so we'd have the FOTL access. It will be at the end of June and very busy. What are the wait times you have experienced?
The longest we have ever waited for a Express line is 15 minutes as macraven said. And that was the new Minion Mayhem ride in August. Most of the time we walk right on. Actually now that I think of it, during peak times of the day we've waited longer for The Simpsons .. maybe 20 minutes? But it had been breaking down earlier in the afternoon and I think there was a back up of people at that point. Generally, you shouldn't wait much longer than 15 or 20 in my experience.
Average time is from walk on to 10 minutes. Sometimes it could get higher. But if the regular line is 60-90 minutes, 15 is no problem.
In the summer we always do the parks in the AM, then go back to RPR and have lunch and pool time. Then we get showered up go to dinner in Citywalk. Then after diner return to the parks. This way you avoid the heat of the day.