Is there any best time of the day to exercise?

When you have time. Anytime is fine. It depends when you can make the time in your schedule. Just be sure to do a light warm up before intense exercise. Prehydration is helpful (1-2 hors prior) which is generally not possible for early morning exercises. Some suggest optimal performance is achieved with midday or early afternoon exercise. Most important just get started any time.
Maybe. The best time to exercise during the day is the time you are most likely to do it! if you have more time in the morning than do it than. If you have more time at night than do it then. From a purely physiological basis there is a benefit to exercise first thing in the morning but you must remember to warm up properly to avoid injuries.