As I'm sure you're seeing from the different answers, weather can be a huge factor in whether or not a mid day break is needed. I've traveled in April, Feb., and August, and quite honestly, DH and I needed the breaks as much as the kids in August. October weather can go either way, I know there was a hot spell last Oct. with temps in the 90's, so keep that in mind.
Another factor, of course, is when you arrive at the parks. If you arrive at the park early, you may be ready to leave sooner than you think.
All that said, on our trip last August, we went at park opening and NEVER stayed at a park past 3pm. (We did occasionally return in the evenings.) Most days it was earlier. Everyone, including the full of energy pre-teen boys, was out of steam by then. On one day, instead of going our resort, we toured the Poly for our break before our dinner at 'Ohana.
Just remember, seeing more doesn't equal having a better time. And, quite honestly, some of my favorite Disney memories are at the resorts not the parks. You may be able to stay all day, but be prepared to leave if everyone starts getting tired/ cranky. You'll have a much nicer vacation that way.
