Definitely for me mornings. Start time isn't until 9:00 so you know it will be late getting off work. A friend who is now retired after 33 years got me started in '94. We would lift in the winter time and cycle outside in the spring then shower and of to work. When I first started I told my friend that there is now way we can do this and then throw pkgs for 9+ hours but after the first week or so I discovered that I had way more energy and spark during the work day than if I don't workout in the mornings. He also taught me to pack a nutritious lunch and eat something every hour of the day (graze) this way you don't go chasing those huge meals in the afternoon and evening. I do get the 3pm crash sometimes, probably because of my rewarding cups of coffee in the morning.
Now I go to a 6am coffee drinking class with a running problem, I run with people of all different abilities and then we meet up at a coffee shack and take turns buying, it keeps you loyal to coming to class (as we call it).
Now that I am 52 with 31 years in as a driver I try to shoot for 8 hours of sleep every night, research tells us that it is very important for recovery and rebuild. During peak I always shut down the gym time and just try to relax when I am not at work.