What chicken wouldn't like grain any way they can get it.
But I pull all afternoon grain when it's past 90 degrees. Its been a 100 here lately. They get ice cubes in their water basins, they drink it and stand in it to cool off. If you have a chicken with heat exhaustion stand them in ice water to cool them off fast. They get ACV in their drinkers in the hen house, it could be my imagination, but it seems to help them handle the heat. They get chopped Cucs and carrot shreds, etc. from the frig or in frozen cubes. They get watermelon and cantalope and so do we. They get cool salad trimmings in the heat of the day.
I do give them grain 1st thing in the morning and when its time to go back to their yard in the evening. I have read so many times that grain heats them up when they digest it that in extreme heat I don't give it to them during the day. Last year I had one hen that had a problem with heat no matter what I did, I was always standing her in water. Some say naw, but I know when I eat oatmeal or corn meal it warms me up. A favorite winter food. This is summer.
Make sure they are cool in their nesting boxes, you don't want a bad surprise when gathering eggs. Yes, chickens can have heat strokes. Our nesting boxes are on the outside of the hen house, so we put hardware cloth on the backside with a door that flops down when I want them to have a screened back side. This way they don't overheat while laying their eggs in the afternoon.