When did Hagrides:
A) Get it's first post
B) Get it's track on site Edit: It appears May 20, 2018
C) Get it's first support
D) Get it's first track laid
Not that all projects work on similar timelines, but that will give you a good baseline.
Simply because this thing won't have nearly as much rockwork, detail or technical work as Hagrid's did.
Edit: So this is 1 month different than Hagrid's. So it needs a whole extra year of rockwork? Sorry 2021 folks, unless Universal just sits on their hands and lets weeds grow over the track, this isn't taking 2 years.