Steve,
As summer is my busy time at work, it is near impossible for me to make it out later in the year. That is why I have to make my trips early.
It gets really hot that time of year too. The kids do not mind, but you better bring your airconditioned underwear. And a camelback!
We here take a break in July and August. I think the average last 100f days in Texas are mid September.
You will enjoy it!