Not flowering

Some are faster than others, but that one is within reason at 13 days as far as expected development - i'd guess 12-14 days since flip to bloom for that autoflower too. You'll just get a bigger yield, because that plant veged longer than a typical autoflower. Really hard to diagnose leaves under any grow light but that one in particular makes it even tougher. If new growth is showing chlorosis, thinner blades, and you amped up p/k like most do in flower, it is likely caused by that. Minor burned tips, as long as that doesn't progress, no biggie. Leaves are perky otherwise. Don't think it's been delayed.. just within normal genetic variation of an autoflower. What stress is there is quite minor, so .. i'd lean genetics.

I think you may want to feed it a bit less. I see some light nutrient burn on the tips of some of the leaves and 1.8EC is a bit high for an auto in my view. I also feel the 20/4 light schedule is a bit much. You should be going off of DLI the 20/4 might be to much. and if its not, you can always move the light closer or increase its brightness/intensity, this will make up the difference if that's an option for you. Pre flowers are in the works and not all plants are the same even from the same batch/package of seed. Autos are known to do w/e the fuck they want and some go into a late Veg and other go into a early flower. Its just luck of the draw. Good Luck!

I see preflowers, maybe excessive Nitrogen blocks her development. Give time, review feeding.