We were given breakfast slots in July, for the first time ever (that was our 4th time at HNY) I was a bit annoyed when I first found out about this as one of the main benefits for HNY for us is that times were not restricted.
But, we noticed that no-one actually looked at them or enforced the times. I don't think we made breakfast at the appointed slot on any of the days, and it was not a problem.
When you go for breakfast, I'd suggest walking straight past the Parkside Diner and go to the end of the corridor and into the Manhattan restaurant. You get exactly the same breakfast items in both, but the Manhattan is a bit nicer. The Parkside is nice, but it's mainly booth seats and I find these a bit of a pain when it's a buffet and everyone has to move to let each other out.