AFAIK it usually ends on the day that the announcement is publicly made. Usually you'll see a few reviews the day or night before then a flood of reviews the next day. My guess is expect reviews by the dozens on launch day (June 6th?) and perhaps some leaked reviews at the end of May.
I could be technically wrong, but that usually is how it turns out. NDA's are legally necessary but have been almost pointless for a good 10-13 years where if you don't do something after someone leaks it you're losing on the page views = money.