True (for some people). The best time is the time when you can do it on a consistent basis.
Scientifically speaking, your body responds best to exercise during the late afternoon when its temperature is highest (body temperature fluctuates throughout the day and is lowest a few hours before waking).
However, many people have difficulty making time for exercise in the late afternoon. The majority of people who exercise consistently do so early in the day, making time for exercise by getting up earlier. Cold, stiff muscles may be more prone to injury so be sure to warm up first.
If you prefer to exercise in the evening, do so at least three hours before bed so you dont have problems falling asleep