Around 5-6 weeks I think
Not likely going to get bigger.. AUTOs... love hate relationship with me. As long as you're not to worried about almost no yield then good ... otherwise they grow like this a lot for me. 1/2 are 10" the other 1/2 are 14" and a few taller ones when I run them. It's genetics no way out of as short smallish plant unless you feed them nitrogen. meh.. I can't stand the taste of weed grown like that ..... to each their own, eh?
I always start them off in the finish containers ... #3 is about perfect... good for the occasional 20" and perfect for the smallies. I run 20 at a time to make up for the lack of yield! I get a decent stash that way.
Organically grown... brings out more of the ruderalis traits IMHO. The smoke tho, good things come in small packages! My 4'11" mom always told me that. I'm going with it...
They can run in the VEG lighting. It's not going to make much difference. When you can put them out on the veranda that'd be where I'd grow em. Can run flower lights at night and bring the little ones in and give them extra... don't even have to do it every day. You wont get hermies on the AUTOs which is kinda weird. I've ran 100s of em and never had any issues other than size and I've done just about everything you can imagine wrong to them. One good trait. They are tough as nails (and pretty), like my Russian wife.
Reason they flowered early was due to the small container. They run the tap root down to find out what the soil is so they know how tall to grow. They hit btm of pot and then they want to flower. Why I start in #3 pots. I could go to #5 but I've tried and the difference ain't worth the extra soil IMHO.
AUTOs ... all about time. Think of then at 2 weeks after sprout they start stretch then flower.
Those tallish airpots should do the trick. G/L with them and don't stress over them for sure. I look at these AUTOs as bonus weed. If they make it to the end ... yay celebrate.