To bring this up (and if I'm wrong, feel free to ignite the criticism towards this statement), I would actually like to point a particular finger..to an unique example of an attraction that opened late, that gained some very positive receptions: Infinity Falls.
Yes, construction be damned, Infinity Falls was a unique example, as it seemed to at-least..my own opinion. And that in a way; the fact that it was bumped from it's Summer spot, didn't harm it. In-fact, the word of mouth for the attraction was actually more than enough to have people come out for the attraction and be busy for a good period of time. It became a hit, even though it didn't even open until after Labor Day.
Now, I'm not saying to expect JW to be not open until after Early September, but if UCW (and, they are given the seeming love being put towards this) want to ensure it's the best that it could be..then I'd be curious to see how locals in the LA area reacts towards this attraction.