I know you need to arrive about 10min early, BUT what if you happen to arrive about 10min after your set time?? Do you loose your spot, do you get to just wait for next table???
I asked the question last year of a cast member. We were constantly running late because of my stepson's obsessions with geckos and his thinking that the combo honeymoon/vacation was all about him. You can arrive up to one hour after your time.
I wouldn't count on having an extra hour to get to all of your restaurants. Depending on how full the restaurant is, and how late your dining time is, you may not be able to be seated if you arrive that late.
We once saw a family turned away from Princess Storybook Breakfast when they were 15 min late for their reservation... and this was at around 9:30 am.
They do their best to work you in, but there is no guarantee that they can do it. Many of the restaurants are quite crowded with all the dining plan use.
They do try to work you in. We had dinner ressies at CRT one time and they happened to be right when the parade was starting. So Main Street was jam PACKED and we were trying to rush through the stores for a quicker route. We were dresed up nicely and people were actually handing us their children to take pictures with (VERY odd). Anyway, we didn't get to the castle until about 30 minutes or so after our time. It took a bit, but they did work us in and even gave us a window seat.
Last year my Mom, sister, and neice were over 30 minutes late for , of all things, our CRT princess breakfast ADR's, and they still seated us and were very kind and understanding about it.