Depending on why you are riding, a shorter ride in the morning can be as effective as a longer ride later in the day.
I'm talking weight loss here. Basically if you've eaten, it takes about 20-30 minutes of aerobic exercise to burn through the energy in the food that has been recently eaten, then you go into fat burning mode. If you do an aerobic workout before breakfast, you go into almost immediately, so a 25 - 30 minute workout before breakfast is as effective as a 45+ minute workout after. Just make sure you don't do too much, because your body can only convert so much in a short period of time..
Again, depends on your goals, but I like that pre-breakfast 8-10 mile ride in addition to my longer evening rides. The pounds are falling off.
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Tom
"It hurts so good..."