What time during the day is the best time to workout to gain muscle mass. morning(empty stomack but eat after) afternoon or late at night?

Best time is anytime: Best time to exercise is anytime you can do so regularly. Worse time to exercise is forcing yourself to become an early bird when you're naturally a night owl (or vice versa). You should eat something (many fans of chocolate milk for post-exercise drink) after every workout regardless of time of day. Don't be overly aggressive early on & get burned out from frustration. Start slow & build up base.