Well, I've just started doing this. Am very overweight, but have recently lost 2.5 stone with weight watchers. Loss is starting to slow down so I thought I ought to start thinking about exercise. I've done 2 sessions so far, and my 3rd week one session will be tomorrow morning.
The first one I did was in the middle of the afternoon and heat wise that was a mistake! So for the second one I got up early (not good in the holidays) and went at 7am - much better! I did find the second session easier but I don't know how much of that was due to the heat.
I track everything using the endomondo app on my phone