The best time to exercise depends on a person's preferences and situation; the time of day does not factor into how efficiently exercise burns calories. The key factor is establishing a routine.
Morning may be the best exercise time for people who have trouble sticking to schedules. This is because they complete their exercise before other events derail them. Lunch breaks are a common time for some people to exercise, particularly for those who enjoy socializing with co-workers. Other people prefer to exercise in the afternoons or early evenings. However, exercising too late in the day may make it more difficult for a person to fall asleep.