We always have a couple of pre-park opening breakfasts. If we have an ADR for 8:00am, we try to be at the bus stop of our resort (usually POFQ) by 6:55am. Usually we arrive at the park by 7:20am or so, lots of time to check in for breakfast reservation. As Maxiesmom mentioned, they are just not as frequent. If it is an early breakfast at a resort, it is a bit more difficult (for example, 1900 Park Fare breakfast or 'Ohana, we are more likely to take a cab) because you would need to transfer to another bus/boat/monorail and I'm not sure how early monorail/boats run.