I’ve always been told at 16 hours for vegetation
If cannabis gets 12 hours of light, it will "flip" to flower, assuming that the plant had gone through enough of the veg stage to be mature. At two weeks, that's very young so it may not flip.
Re. the photoperiod - I grow my photos in veg at 24/0 for the first few weeks and then 20/4 until flip.
If your light schedule is 16/8, the result will be that your plants don't have the opportunity to grow as much and they will not develop as many roots, stems, and leaves as plants that receive more light. Crop quantity and quality will be reduced compared to plants that receive more light in veg.
When I grow autos, I start with 24/0 and then drop to 20/4 for the remainder of the grow.
Since light is the only way that plants can generate food, the more light, the better, up to the light saturation point. As long as light is the limiting factor, you should shoot for 1000µmol of light for your plants. Some strains won't grow at much over 800µmol but I have grown my autos at 1000-1100µmol and my last photo grow was quite happy at 1150±µmol