On days of 95 and up I horse my horses off at 2-3 pm and after their pm feeding 7pm. If it's really bad in the mornings I might add another hosing off at noon. Also, If it's really hot, I don't sweat scrape.
My barn is like an oven in the summer so I prefer to leave them out during the day, making sure they have access to shade. Just bringing them in for feedings. They have a fan in front of each of their stalls which helps a little bit.
I end up refilling their water troughs in the mornings and evenings because they prefer colder, fresher water. I just want to ensure they are drinking enough.
Oh, and I also add electrolytes to their feed. My horses manage to sweat a lot even without exercise. Some of my horses don't get grain in the summer so I just add their electrolytes to 3 spoonfuls of applesauce instead.
I'd say the best thing you can do is to just check on them frequently. Severe heat can affect them so differently. I have some that do okay and others that suffer greatly!
Good luck! This is when I want winter.. PRONTO! haha