Well, when I commute (about 6 weeks out of the year) I leave as soon as the sun is up some, first at 5:45 and now at 5:30. It's about 14 miles, with only one hill, right at the end. But, it's a lot of false flats and rollers and believe me, my speed is about 2 mph slower than the trip home. Now, I have been exercising at the gym at 5-5:30 AM for almost 30 years and I never felt this bad in the morning. Right now, it's still in the 40s at that time, maybe 50s/low 60s by the end of school. I think the temperature plays into it, too.
In the summer, I'll ride (for fitness) at 5:30 AM on days when it is going to be in the 90s and humid. I don't feel as bad then.
I eat a small bowl of cereal with yogurt and fruit before I go. Then I eat a Luna bar or half a soy nut butter sandwich when I get there. I eat a slightly bigger lunch on the days I commute home. I also have more carbs the night before.
My best time to ride is from 10 AM to 3 PM.