It's best to exercise in the AM if you can, according to the research types. Exercising too late in the day interferes with sound sleep. Exercising too soon after a meal will upset the stomach. In Chris Carmichael's new nutrition book, he provides recommendations on meal size vs. time before exercise.
Before retirement, I got up @ 0430 to exercise and get to work before 0700. I exercised before I ate breakfast, but I did gulpdown some fast burning carbos like jam. Now, I still get up the same hour, but I have time too eat and digest a little. That raises the energy level somewhat.
Too maximize rest which is a critical element in any training program, it's best to rise at the same hour every day, seven days a week. If you stay up late the previous night, you'll still have the max energy during the day if you get up at the same time. The extra fatigue will best be handled by going to bed earlier the following night.
Al