We were there from 5-28 to 6-6 and the heat was horrendous. The high was in the 90's with high-humidity that made it feel like a sauna. I'm accustomed to the heat (Texas isn't exactly chilly in the summer) but the heat combined with the humidity, crowds, pavement......you get the picture. It was really, really hot. Most people had personal misting fans - they cost $17.95 filled with ice water at the parks.
We left the park each day by noon or found indoor places to enjoy the AC. Frankly, we had a hard time going back to our pool -I was anxious to get my girls out of the sun.
We did have a few days where it cooled off at around 5pm. I think there were only 2 days that we did not have an afternoon shower. The cloud-cover before showers was always a welcomed reprieve from the sweltering heat of the sun.
Drink lots of water, wear lots of sunscreen, take fans, wear shoes that let you get your feet wet - we all ended up wearing our Keens - very comfortable to walk in AND the added bonus of allowing us to wade through any form of water that happened to sprout up from nowhere. Our althletic shoes were hot and heavy. Pouring ice-cold water down your legs and splashing your arms, face, and neck was a nice refresher.
Have fun!