How late would a 3 year old stay up at Disney World?

I am trying to figure out the best time for our first visit with our baby daughter. If we go in April she would be 3 months shy of 3 years old, and if we go in October she would be 3 years 3 months. We have been to Disney many times but that was before we had kids. I would like know how late she could stay up at Disney World. Most of the fireworks are around 9pm. Would she just fall asleep in the stroller or would we have to go back to the resort for bedtime, which is probably going to be earlier than that? She would be charged for Mickey's Not So Scary Halloween Party, $55...but it is from 7pm-12am.. would she be awake?