The number was given back in 2016, and I imagine some worlds might be 2-ish hours but I can’t imagine something like Olympus being done in just 2-ish hours. We have to climb the mountain, fight the Rock Troll in Thebes, fight the Rock Titan, and get to the Heavens.
Combine that with exploration and cutscenes, the first visit to Olympus looks like it will take quite a few hours to get to the end of that world. And that’s without returning for mini-games, collectables that require end-game skills, the rare heartless, and more.
I can see something like Tangled being 2-ish hours, since that area is a lot more straightforward than Olympus and you just need to fight through forests until Corona, and shortly after leaving the town you go towards the end boss fight. There needs to be something to happen for Sora to be yelling for Org XIII to show their self (scripted fight against Nobodies?), then you meet Rapunzel and Flynn, escort them through the Snuggly Duckling with a mini-fight in the canyon, then through the forests to Corona, and finally to the final boss.
It’s a lot more clear how Tangled most likely will go and how it fits into the number Nomura gave two years ago but some world like Olympus is a lot more unclear since it’s wholly original and hard to see how it all connects together.
20 hours would be incredibly short for a game like KH3 and something I don’t expect. DDD was 30-ish hours on my first playthrough, and that only had seven playable worlds in it. I need KH3 to be long and delicious.