It doesn?t really matter when you work out unless you have a specific goal in mind. If you want to maximize fat loss, then you should work out right after you wake up on an empty/mostly empty stomach. This way you only have fat as a source of energy. Well, not really, but just go with me on this one.
My workout is dependant on my work schedule. Some days I open, and some days I close. If I close, I work out in the morning, and vice versa. I do find it difficult at times to motivate myself to the gym after working all day, but that is just a motivation issue. I went to the gym every day at 6:45 pm last summer, and nothing bad happened. I felt like I slept better since I worked myself so hard.