I have chosen to do the same thing, but our ceremony is at 5pm, and I've heard that it cools down a bit in the evening. I read a review on Tripadvisor from a bride getting married in the exact location we were, and her dinner was in a partially outside restaurant at night. She said that it wasn't air conditioned, and it didn't need to be.
I would make sure to tell everyone to make sure they bring their sunscreen (obviously) maybe some parasols, or suggest to the older ladies a wide brimmed hat?
Good luck!