Ive heard you shouldn't exercise an hour before eating and at least a few hours after eating (for obvious reasons I think). Ive read the optimum time to exercise, if possible, is after waking and before eating breakfast as all your sugars were burned up when you were asleep and the body will be burning fat during the morning workout. Ive been working out after work and before dinner and have been just fine. I think to answer the question, I think its whatever time is most convenient for you and when it'd be most comfortable to do so.