To be honest, I think they could probably start work next year, and be ready by mid 2022.
Keep in mind, IOA began construction in 1997 and they officially opened the park, along with Universal Citywalk; Portofino Bay and parking. I don't see it as impossible, and that they could easily begin work next year and they would have four years of development from infrastructure to installation of the park. It's not impossible, and that I would imagine it's all waiting on the issue of the Stan Thomas lawsuit (which I expect that to be quick).
But perhaps discussion of when the fourth gate and other things being ready can be taken to a proper thread?