Just a thought but working out first thing before any sugar intake what so ever would have to burn "stored calories " in my opinion. I believe that is also one of the beach body principles, but I am not sure.
It doesn't matter what time of day you engage in physical activity. Truth is if you are trying to lose weight or drop body fat it is about calories burned. Intensity is the key to more calories burned. 20 min of high intensity cardio will burn more calories than 20 min of low intensity cardio. Time of day, don't matter. I feel as if I am more active mid afternoon, so I get my cardio then.