someone cleared that up for me on another thread... BUT.. do you think the chemistry happens that fast in the plant???? does it in nature?? does the day go from 8 hours of dark to 12?? it happens gradually.. it's the 12 hours of darkness that triggers the flowering. SO to each his own. I would say somewhere in the first week of flowering is when it actually starts.. which isn't a really a big deal if you count those days..
Unless any of you created the first MJ plant in a lab then you really don't know for sure..