2023 is a long way away but I'm thinking they will want it open in the first half of 2023 for that summer crowd. That's 3 and a half years.
You're talking about 6 months before infrastructure can even start. Roads need to be built along with parking, final grading and all the back of house stuff (Offices and warehouses)
You'll have all the infrastructure which includes plumbing, cooling and electrical, look at Volcano Bay, they spent about a year getting the plumbing done alone. This isn't just infrastructure for a park, this is a fully functioning 21st century park that needs to be future proof for at least 100 years plus any future expansions including a water park, possibly a 4th dry park, multiple resorts, and an entertainment district. I'm also getting the feeling that this will also be a multi level park that also adds a ton of new challenges.
Once it goes vertical, it should be a quick build after that for about 2 years and they have the luxury of not having to restrict building for the 12 hours a day that a park is open to the public.
The problem is that there are a lot of stages and they can't overlap. Add on top of this, you need a ton of labour and designs are still in flux.