I ride on a trainer in the AM before breakfast so that I'm burning fat for fuel instead of using blood sugar. I wouldn't do this out on the roads though, it can get rough on the system and if you pass out from lack of blood sugar it could get dangerous.
Just so you know, a 150 pound person biking at 14-16mph for 30 minutes burns around 300 calories. That's not even a Quarter Pounder w/Cheese (which is 510, BTW).
For calorie counting, go by time, not by miles. 30 minutes at least each day.
Plus riding in the AM will jump start your metabolism for the whole day. You will burn more calories over the day, with diminishing returns over the hours.