It's actually been something that Hollywood has done twice in a decade, with both TWDA and Kong 360 opening around the time of Fourth of July (even if it's off by just a few days). And in a sense, there shouldn't need to be as much of a worry with softing this on a longer period of time, as most of the track that was there should still be fully present (As the attraction did get retracked two years ago if I'm not mistaken).That feels like the worst-case scenario.
I don’t have a crowd-calendar in front of me, but I would assume that Memorial Day weekend kicks off the official beginning of summer and July 4th weekend is the summer peak.
It would be a mess to try and open your new hottest ride near the busiest weekend of the summer. I would think they would want either want to open the ride 2-3 weeks before the 4th or wait to do softs until after the 4th.
Post-July 4th softs would mean a late-July grand opening and that’s so late.
Not to mention, Universal Hollywood's summer season as somewhat mentioned by Snark, doesn't start until mid to late June. And with the current speed that they are at with Jurassic World, doing daily testings and finishing exterior works, it would be very possible to see it come around at that time.