Where you going to/from? I'm here in Kansas and it has been brutal. Worst week of heat in the last few years. I ride early AM year round so I relaly don't have to adjust much. But it is odd starting out at sunrise and it is over 80 F. Still, my advice is also to start at crack of dawn and ride. It is tolerable here until close to noon. That can get you nearly 6 hrs of ride time.
Spend the rest of the day in the cool, recouping. It's gonna cool off here later in the week and improve next week somewhat. Last several days have all been very close to 110 F or more. That is brutal by any standards.