Plant A in the above pics has distinct yellowing o...

I recommend lowering the nutrients a bit on her and doing a water change, if you don't do 1 regularly. Doesn't seem like 1 deficiency. Could be excess salts built up in the reservoir locking out nutrients even though PH is in range. She seems stressed and that's why she is a little slower, that and pheno of course! Do the roots look healthy? Putting her in darkness wont make her flower any faster if its good genetics. Even a photoperoid 12/12 from seed wont start showing buds until its mature enough (typically 3 weeks). Guess that's why some growers dont consider flowering stage til they see budlets. Good luck and happy growing! 💪🍀