You flower at 12/12. You vege at 18/6 or up to 24 hr light.

If you start your seed at 12/12 they will take 3 weeks to a month to declare Your seed will be growing 12 hours instead of 18 that adds up to 6 hours each day that the plant is not growing. No photosynthisis = no light= no growth. Now that extra 6 hours of growing time may not seem like much, but then you multiply it times seven (days in a week) you lose 42 hours of growth a week. Now multiply it by the four weeks and you have lost 168 hours of light time. But you know the sex of your plants. And then into the vege room we go.

But now you must make up that time you lost. 168 hours. You have females but the plants are not near as big as if you had gone with your normal 18/6. Plants that are preparing themselves to flower must now slam on the brakes and swich back to vege. That takes a week or more. You also owe 168 hours of light. Thats about 9 or so days just to catch up. In a perfect world you are behind schedule to the tune of (at minimum) 2 weeks.

So you lose two weeks of yield or in our perfect world your plants need two more weeks to reach their normal hight.

I live in Hawaii. I have a room but it is seldom used. We have one long season and two short season. Short season is when I pick my mothers. All under sunlight. I can go from seed to bud in 100 days. Not large plants but each gives me a sample. Pick what I want to save, leave 4 bottom buds, and it goes under 24 hr light to force it out of bud. Then I take my clones.

Hope I made sense and good luck.