Does anyone know, can I veg them for 6 weeks? Will they only start showing sex when the light cycle changes? When the description says 9 weeks flowering, is that from when you change the light cycle or when they start showing sex?
No one seemed to answer your questions so here ya go:
Yes, you can veg any non-auto-flowering plant for eternity. Some of the big seed houses will keep a mother plant in veg for years.
Plants can show sex before flowering so yes they can show sex when vegging. Plants will begin to grow pre-flowers about 4 weeks into full veg. About 2 weeks later you might be able to tell if its sex and a full month later you should have no problem sexing. The first time I let a plant stay in veg for over a month, about two months worth, it showed itself to be female. I was so happy.
Oh, I did have a 12/12 from seedling that took 2 months to show sex while another 12/12 from seedling, grown at the exact same time, showed in 2 weeks. Go figure, bag seeds.
Generally speaking flowering begins when you put them under 12/12. Technically speaking the full flowering phase starts few days, up to two weeks, after you put them into 12/12 light but everyone just counts the start of 12/12 as the start of flowering so you should too. I think that's why they always say add a week to the flowering time to get more out of your buds. They really are a week younger in flowering.
I wonder if the real, old school growers count flowering when actual flowering begins, when the little buds start forming and you have a bunch of white pistils shooting out all over the place.