whats the shortest time i can veg an photo and still get an oz

If you want quick and only an Oz then stick to auto. If you want more and learn training and the likes another few weeks won't hurt. Especially if you have some ready to flower when harvesting. Even better run a flower tent and run an auto with the vegging plants. Perpetual is your aim. I harvest one plant every two weeks. A different strain. I do lose out and it makes for more work

If you start with cutting, you could reduce the veg period to 2 weeks. You also can start directly in flowering, but I don't recommend as you can have variable results. Also, the advantage of non-auto, is the control you have over the entire culture to push all your plants into flowering at the same time. The shortest time I've let my plants in veg was 4 weeks, without training. But the best to me now, is 7~8 weeks, with rotations between 2 grow spaces: when I harvest the plants from the Flo space, I put the plants from the Grow space into the Flo space (and start flowering) and use the Gro space to dry the flowers before starting to grow again. In result, I can harvest every 2 months, and because I take the time in grow to have big well trained plants, I easily hit the pound of dry flowers each time. I find it way better than rushing the vegetative period and I can achieve 3 or 4 rotations a year (I don't grow in summer, too hot and I'm usually not at home at this time).

If you grow in coco or dwc you could probably do it easily with a month or 30 days veg then flipping to flower depending on your skill level. 👍🏻

I'm going to be completely honest with you this is nearly impossible to answer. There are a lot of factors that will contribute, your experience, the strain/pheno, your lighting arrangement, and the grow space allotted.

So to answer your question, Veg for at least 30 days then go 12/12. You can’t initiate flower any sooner than that. Be aware that - Depending on genetics, it may take a week or two after day 30 to be mature enough to flower.

You should be able to get an oz from any photoperiod if grown in decent conditions. Going 12/12 from seed is losing weight. Only do it if you HAVE to veg in 12/12. Photoperiods won’t be mature enough to flower until they’ve reached 30-45 days of veg. Knowing this - run 18/6 or 20/4 until day 30-40 and then flip to 12/12. You will have more veg growth and yield more than going 12/12 from seed

You can run a straight 12/12 from seedling and you'll still get close to a month of veg time before it flips. Now what you're able to achieve from that schedule will depend on method and strain and your lights. If you run a heavy producer in a hydro setup, you could probably meet/exceed your 1 oz per plant goal.