The majority of people who exercise consistently do so early in the day. It is easier to form the exercise habit through morning exercise. • Fewer distractions and schedule interruptions. • Can make time for exercise by getting up a bit earlier. • Raises your heart rate and metabolism to burn more calories earlier in the day. • Gives a feeling of physical energy for hours. • Improves your mental acuity for hours. • Cooler temperatures in summer. • Air pollution is lowest in the morning. • The body adjusts to your exercise time, so if you are training for a morning sports event, train in the morning. This was taken from an About.com article, I hope it helps!

It is best to exercise when your mind is most active and alert, whatever time of the day that is for you.  Just make sure that you have a block of free time and that you will not be getting continuously sidetracked.

Depends on your status and where are you ,i think

Seen from a scientific perspective definitely in the late afternoon or evening, around 5-6pm. The best time to improve your bodies fitness.

Morning ,i think. There is fresh air.