Just thought I'd add my experiences!
We stayed at the Poly in '04, I think it was Rartonga building - we walk to the Epcot monorail at TTC - no problem, short walk... and we get up the walk just as the Epcot monorail left.... and so then we have to wait for it to return, and I think that took about 20 minutes... it was the longest 20 minutes, I had planned the time down to the minute, but didnt build in the "we just missed the monorail, and have to wait for it to come back"!!
So we got thru the turnstyle (our names were indeed on the clipboard, and we were let in early) and literally took off at a very fast pace - again, I'm thinking it was 8:30 our adr time when we got thru the turnstyle, and it was our first trip to the world, and I hadnt been online, so I wasnt too prepared!!
We did get there at 8:45 ish (I'm fuzzy with the times, but I do remember getting there after our adr time!!) and there were people seated around the entrance to the restaurant... I gave them our name, and they took us, right then!!

We were seated in a lovely alcove, with only 4 other tables (maybe 5 or 6, it just felt so quiet compared to the 2 main dining rooms we walked through to get to 'our' alcove!!)
So, no worry, if you miss that monorail, you wont miss the Princesses!!!
(PS dd loved the food there - typical breakfast fare, but I think the skillet helps keep the eggs and potatoes warm!!)