sometimes it's a as early as a couple of weeks before 12-12 Sometimes is a couple of weeks after. Usually within that first 7-10 days. That's been my limited indoor flowering experience. I have usually grown outdoors and it depends on the calendar. Usually between Sept 1 and Oct 15 here at 45* latitude. Many variables such as strain and weather conditions effect the date. You can usually tell before hand to within 2 weeks.

Shovelhandle