I would not do it. And yes, I have a child.
One big reason is that I know that my daughter would have gotten so hot and frustrated and tired waiting for that long, that by the time we actually got to them, she would not have enjoyed it. So what's the point?
Plus, the truth is that I'm not willing to stand for four hours in rain or heat on hard surfaces trying to ignore my need to go to the potty while also trying to entertain a kid and keep them enthused when the reward is a 5 minute interaction. Sounds like a circle of hell to me. Plus... Maybe because I've worked with abused and underprivileged kids in my career, but the notion that my kid is somehow deprived or their expensive vacation that costs more than some people live on for an entire year is ruined because they didn't get to meet two girls dressed up in costumes is
Basically, I think it's important to manage expectations and avoid promising something you may not be willing or able to deliver, including on a vacation. I did not promise my kid anything big that could become the One.Big.Thing she focuses on to the exclusion of all else on a vacation because although I do my best, there are times when situations out of my control can create disappointment. I didn't want to set up a situation where their entire focus is on something out of my control. I always told my dd that we "hoped" to do something, but I always cautioned her that "there are no guarantees".
One reason I do that is because my parents had a tendency on vacation to "talk big", but "deliver small". Sometimes it was because they were chronically careless and had gotten the day of an event wrong and we showed up and it was the day before. Sometimes it was because they decided they'd rather do something else. Sometimes it was that it cost more money than we had. Etc. Until we learned to discount any promises from them, my sister and I felt that most of our vacations were ruined because we did not get that One. Big.Promised.Thing. Even though there were times when we got Some.Other.Big.Thing. It was much better when we learned to just take each day as it came and enjoy what we actually DID get, rather than getting disappointed about that One.Big.Promised.Thing.