We had a breakfast reservation here on Christmas morning ( I was so proud of myself for getting this one!) and when we first checked in about 1 hour early, one lady said no, cant get in early. No biggie....until when we started to walk away, a dad walked up with the same size of family we have and asked if they were accepting walk ins. They said yes, and took them right in. So I went up and asked a different lady who got us in right away as well.
Sooo, I would have to say just check in when you are ready and see. wont hurt to try.