Some people do a 24 hour light schedule and some plants handle it well. However me personally, I think plants do well with with some dark period. Ive had plants that responded poorly to the 24/0 and got burnt leaf tips. whether you choose a 20/4 18/6 is your opinion, but i wouldn't do less than the 18/6 with an auto, and that can be for the whole life of plant. During the flowering phase however if you were attempting to push the plant to mature more or faster, you could possibly go to a 15-13 hours of light.
Happy healthy growing, hope your 2nd seed sprouts. ✌️