Good topic. Some quick first thoughts:
Method 1: likely to bonk because of low blood sugar. muscle glycogen is still full the next morning, but liver glycogen will be more depleted because it is used to stabilize blood sugar during the night. So it’s likely that low blood sugar (brain bonk) occurs.
Method 2: is this with breakfast? ether way this training regime will be probably more beneficial for training adaptation. As it has been shown, that the longer you wait with replenishing the glycogen stores in your muscles the more mitochondria and other adaptations for aerobic fat metabolism will occur. Bonking in the second training session is likely. Probably both ways.
BUT: isn’t it always the brain that senses fatigue and causes you to slow down or even bonk?
Good fat metabolism plays a huge role. And also the ability to produce ketones.
The 80/20 “rule” is only defined by intensity. If you train below AeT it doesn’t matter if you fasted before or not. Fasted maybe feel harder, but it’s not higher intensity (probably even lower). That doesn’t mean that the stress on the body isn’t higher. You don’t count it as higher intensity, but you have to be careful about the training load.
I don’t have any exact numbers in mind, but muscle glycogen is never totally depleted (even with a ketogenic diet). It’s always the brain that senses if something is getting low or out of balance. As it senses this as a risk for the body, it shuts down before serious damage occurs (in most cases)