I honestly wouldn't be surprised if they're starting now. If what you guys are saying about it opening 2017 is true, then it needs to start soon. Even if it's a whatever park, it's still an entire new park that needs to meet Universal's standards as far as theming goes and Teebin has hinted at this huge Volcanic structure. I feel like it will probably take at least 2 years and even if they finish the park sometime around late 2016, Early 2017, no one opens a water park in the Fall/Winter anyway.
The earliest they would open it is for Spring Break 2017.