A lot of speculation on this thread. First of all, plants do fine without dark periods during veg.
I've ran 18/6, 20/4, 24 on veg and have noticed very little difference with the 20/4 showing slightly better results and I mean slightly like a day or two faster. But I noticed very little difference between 18/6 and 24. In the summer heat I'll run 18/6 to help combat midday heat, and in winter I typically run 24 to keep the warmth going.
Second, people are commenting on nirvana strains but have not ran them, how does that work?
Oh, I know they're cheap so they must not be as good as a $100+ dollar pack. Just like if I buy a pair of Nikes I could jump 5ft vertically, but if I send less money on converses, I'll only jump half of that height.
I've ran several nirvana strains, top 44, crystal, blue mystic, Ice, PPP, ak 48, swiss miss and a couple others that I can't recall and next to top dollar seeds they fair just the same.
For example my top 44 keeper in 2004 had a raspberryish flavor and was super potent. I only paid $25 for 10 seeds, while my buddy spent $320 on ten Jack Herer seeds from Sensi seeds that same year and dude would sell his Jack buds to buy my top 44. It's all in the luck of the draw.
That being said I have little to suggest to the OP, 30 days and your seedlings should be much larger. Goodluck