No, it’s not a stretch at all. The Hagrid ride regularly hit 10 hours went it first opened.
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'Harry Potter' fans battle crowds and lightning in 10-hour wait to ride new 'Hagrid' roller coaster)
It is not far fetched in the least to think Disneyland’s first ground-up e-ticket ride since Radiator Springs Racers—or, if you really wanna get technical, the first ground-up e-ticket since Indiana Jones—would attract crowds of that magnitude. I won’t pretend to know what the ride’s capacity is, but I do know this: The day I went, the last boarding group was 105, according to a sign outside of the ride at about 9pm. I checked the app, and they were only boarding group 105 at that point, meaning they likely would have boarded all groups well before the park closed. So naturally, I asked “Will there be a standby line after that?” And they said no. But there’s no reason there couldn’t have been one. The ride ran successfully enough throughout the day that they boarded the 88 guaranteed groups, and then all the remaining standby groups that weren’t guaranteed, and they still had a few hours to spare.
So idk. Take the capacity of everyone who got to ride the ride that day, add in the X amount of people who would have happily stood in a standby line after all the groups had boarded (without forgetting that there definitely would have been a line to get into that line if there was even an inkling of a possibility that it could happen) and I think you have a ride that can clearly operate at capacity and would have a standby that could easily touch 12 hours, if not more. For one reason or another, Disney decided this was the most convenient and efficient way to do this, and it’s hard to disagree. My experience was utterly seamless and efficient. I guess that’s a privileged position, but it’s still the truth.