Yeah, I got that. But was there a specific timefrage mentioned so that we can know when he flipped?
Not really, no. We just have to extrapolate t from the flashback as theres nothing else to go on. In in Rey look about 8, and I think shes meant to be playing someone about 18, so assuming that Rey was taken to Jakku when Kylo flipped and killed everyone, that gives us around a 10 year timeframe.
It's all speculation though, until we get the full story.
Of course, it doesn't have to mean that she is Luke's daughter. I wouldn't mind if she is, because I would be somewhat sad if Luke's and Leia's legacy is to release a mass murdering Psycho into the universe.
Well they came from a mass murdering psycho... Currently the Force sensitive Skywalker family member tally is skewed towards the Dark Side by 2 to 1.