A video on the whole project seems to show two openings: June 30, 2019 for the water park and December 29, 2019 for the rest of the park. Also shows a few renderings of the park itself.
Overview
Themed Areas
Water Park
Garfield Beach
https://www.weibo.com/tv/v/GfOkcoUsH?fid=1034:382cce679bf3b217b516f779a2add069