From my experience, it changes and there really isn’t a set in stone time. What I do is veg a regular seed out long enough to take clones from. If they’re not showing male/female preflowers, I set the clones to 12/12 and go from there. if male, I toss the “mother”. If female, I keep on truckin.
That’s what I do and what works for me. There may be easier/better methods.