I had read that a plant needs to veg 6 -7 weeks b4 turning to flower.
Yep, correct. The plant needs about 6-7wks vegging from seed to get to sexual maturity (displaying preflowers at nodes) before you can even determine sex.
Not sure what you're going to get on just a few weeks of 12/12 from seed sprout. A sexually immature plant won't be of known sex and may not develop floral clusters, of either sex.
While the clones in my op don't get any vegging time per se, the mums they come from are constantly in veg. You have to remember that my mums were sprouted from seed some years ago, vegged to sexual maturity, then sexed. The female lineage lives on of course.
All the cuttings taken from mums post sexual maturity will themselves be sexually mature- and of the same, known sex of the mother.