In the early morning your blood glucose is low because dinner was so long ago, and you won't see any benefit from breakfast unless you had it two hours before the run. Also your body temp is lower after sleep which means your muscles fatigue faster and aren't as flexible, including your lungs. I HATE running in the morning and admire anyone who does it.
I admire anyone who does intervals in the morning. There are so many better times in the day to do it :)
I guess I've earned some admirers the last 2 days then ;)
Intervals are the best in the evening around 6pm after having nachos for lunch. Guaranteed success.