If you want to plan around it, I would say later in the year. And planning with the hell bent intention of it being open would probably be a huge mistake (based on avatar land).
However, if the current cycles hold, Star Wars Episode 9 will come out in December of 2019. I suspect that there will be a big event around the last of the "original 9", that includes the opening of Star Wars Land, Re-imaging of DHS to Disney's Hollywood Adventure (or whatever they will call it), and the opening of the CBR/Gondola stuff.
The one saving grace, imho, about 2019 is I think Disney will be (is in) a hurry for star wars land, and even toy story land, as the studios is just so decimated. And You have a star wars movie and Toy Story 4 coming in 2019.