Whe to finish growing a plant if I want to obtain seeds, not smokeable weed?
It sort of depends how many seeds you wish to grow. If you want as many as possible allow the plant to bud for three or four weeks. Then bring a flowering male near her and shake him a little on her. Let them mingle for a few days and seeds will start developing.
If you just want a few dozen seeds then keep her budding for 6-8 weeks. Trim off the really ripe buds. Then repeat the pollenating I described above.
Keep large sheet cake pans underneath your plant. Seeds can be picked, but, many will ripen and drop in the pans.