Interesting article about that best times to exercise follows your circadian rhythm.
It Matters What Time You Exercise: Muscles Have Circadian RhythmRegarding Fasting:
Morning exercise also makes it easy to exercise while fasting, which will amplify the benefits you receive. Research has shown that exercising on an empty stomach is useful for preventing both weight gain and insulin resistance. One of the explanations for this is that your body's fat-burning processes are controlled by your sympathetic nervous system (SNS), and your SNS is activated by exercise and lack of food.