Twice A Day
For maintaining muscle and quality training, I believe in the art of training twice a day whether its in the afternoon and evening or morning and evening. If my energy is good i'll work out sometimes 3-4 times in a day but two is actually very good to do. You don't have to do hours upon hours who really has time for that? That was the ideal for Charles Atlas and other athletes of that era.
If you only one session for the whole day that's great at least do something. Do some energy drills or Push-ups & other exercises in a 15 minute period in the morning and do another one after coming home from work; chill for a bit, eat up and then train after digesting. This type of way helps the muscles stay fresh and can help give you some quality sleep. Don't train so hard you'll be hurting just get enough to where you're knowing you got some work in and its helping you die down but have some energy left for those endorphins.
I like to sometimes do Bridging at night to help me get those endorphins going and feeling so good it helps me pass out. I might do DVR's at night which really helps the blood flow to the muscles and energizing the body while it brings everything down to help fall asleep. Training a little after waking up gives you that get-up-and-go feeling of supercharging the body and get those impulses firing for the day. If you can get a small increment of training on your lunch break go for it but don't waste so much energy you can't function for your second half on the job. Power up twice a day and you can't go wrong.