12/12 from seed is pointless IMO because the plant isn’t mature enough to transition until about three to three and half weeks. So you should always plant to veg for three weeks before flip so as to not sell yourself short on your yield.
I was reading on another thread where Doc Bud said he doesn't flip until the plant is showing alternating nodes. I don't know if that is a sign of sexual maturity or now, but I will start paying attention. Though generally it doesn't matter since I tend to veg my plants for around 8 weeks or longer.