Hi Felicia,
My family is trying to figure out our itinerary for that day, too! We're very excited that a visit we planned months ago coincides with the 24-hour
Monstrous Summer kick-off.
We've been known to spend as many as 14 straight hours in a park, but even we don't expect that we will be able to hang in for the whole 24 hours (though we may try). I think you have the right idea, especially since your children are relatively young: hit the park early, then take a long break either midday or in the late afternoon, and return after dinner.
Extra hours in the park won't be as much fun if everyone is exhausted and cranky, so a rest is going to be imperative,
It's hard to know what the crowd pattern will be that day since this is a rare event. But I expect that it will be relatively crowded since lots of people will want to be part of the fun.
My daughters are older, much more accustomed to sleeping late and staying up late so I expect we won't return until 9 or 10 p.m. and will plan to stay as late as we can. You will want to gauge your children's stamina patterns and make your arrival and departure plans accordingly. If they are early risers normally, you may want to shoot for the 6 a.m. opening time.
Disney hasn't released all the special events for May 24 at Magic Kingdom yet. I'm going to watch the link the Monstrous Summer I provided above for more details as the day gets closer.
I hope that's helpful. I hope your family has a wonderful time that day and throughout your Walt Disney World visit. Enjoy!
Wilma