The bottom line is a calorie burned is a calorie burned, whether it's in the morning or evening. Choose a workout time that fits into your schedule. If your mornings are crammed, a more realistic plan for you may be to exercise during lunch or in the evening after work or dinner. If you want to burn fat, you need to do 40-45 minutes of moderate to intense exercise at least 4 days a week, no matter what time of day you decide to do it. Scheduling your workouts as appointments can help you to stay on track. You can also break your exercise into segments. Two 20 minute segments are just as effective as 40 minutes all at once.