Morning may be a convenient time for some people from a schedule perspective, but cortisol is very high when waking and decreases throughout the day. Not only is cortisol catabolic, it can increase the chance of injury during a workout. ~6 hours after waking is supposedly optimal, as your cortisol has dropped off since waking and your testosterone starts to peak -- this affects muscle protein synthesis. With that being said, exercising is often better than not exercising.