We went June last year (June 9-17) and it really wasn’t bad for us (we had gone December 28-29 the year before so that probably had something to do with the fact that it seemed so light). The longest posted wait I remember seeing was 2 hours for Radiator Springs Racers but other than that, peak times had 60 minute waits. But if you plan ahead and do rope drop, stay late, and get as many Fastpasses as possible (purchasing Maxpass would allow you to get more), you can do a lot. I never waited more than 45 minutes probably and the only reason I waited that long is because I could stand it and I just wanted to repeat my favorite rides multiple times. As far as grad nights go, don’t worry about it. The 2 least crowded days of our trip were grad nights and they don’t happen a lot of the days of the week. Just plan ahead and you’ll be just fine.