I think it'll be too much.
The last two trips we did the early early flight. Up at 3am, 6am flight, etc. First trip, we went straight to MGM for the day. Suitcases in the car and everything. We had a 5pm reservation at Brown Derby - were so exhausted we went in an hour early to see if we could get seated earlier so we could get to our hotel earlier. While waiting, my DH fell sound asleep on the sofa in their small waiting area. He was completely oblivious to the chaos around him. We mustered through dinner but barely made it.
Second trip with that early of a flight we wised up and chose to not hit a park that day nor make a dinner reservation. When you get 3 hours sleep the night before, have some jet lag, and the tiredness that traveling gives you, it just wasn't worth it. We wandered our hotel, grabbed a quick bite at the hotel, sat in the hot tub, and got to bed early so we could make it the rest of the week.
WCC is not fun if you're cranky and tired. Or maybe I'm the only one that gets cranky when I'm exhausted and had no sleep? I would not find the WCC antics amusing if I'd slept 3 hours the night before. If it's something you want to really experience and get into, I'd plan it for when your family is at their best and ready for some fun.
If there is no room in your schedule for it later in the trip, you could keep the reservation and decide that day.