I asked this question this week on the Walt Disney World Moms Panel because we have an 8 am ADR in November. The answer is TAKE THE BUS. Apparently the parking lot does not always open early, and if you have an early breakfast, the Disney buses are the only mode of transportation that will actually get you into the park early for sure. It seems really stupid to me - what if you aren't staying on property. They don't tell you when you make the ADR that you might not be able to get in the parking lot! Our ADR is on a day when the park opens at 9. The lot will probably open between 8:30 - 8:45. That's right, 30-40 minutes after our reservation time.
We are staying at POFQ, too, so let me know what time the character breakfast bus gets you there!