I've bowhunted the past two archery seasons pretty close to the milk.
I went opening week last year and temps were up to 110f during the day and at night they would fall in the low 30's. Fire band was on so campfires weren't allowed. Saw herds of elk each day and I plan on being back there this year but I'm not going to go as early due to the heat. I'm going to wait around the 18th and hunt the rut and it'll be a little cooler than.
You guessed the game activity right, first couple hours in the morning and last couple hours of the day is when it was most active. I used the afternoons scouting and fishing and trying to stay out of the sun. If you have a tent it could be as hot as an oven so find some shade, and thats not always easy to do. Good luck.

Bobby