Yes you can, I had to do that when Attitude gave those G13labs quicksilver beans away a while ago and my flowering area is on 12/12 of course. I think they might take a short while longer and maybe yeild less not getting as many hours of light but I still got over an OZ of nice bud of it
I was using large tubs with 4plants to a tub. I got a bunch of free seeds from attitude,well one was an auto I didn't notice. it started budding under 18/6 of course but instead of transplanting it I just put all of em into 12/12. way smaller than the photoperiod plants but nice buds just the same.
600w HPS I didn't want to flower them under just my veggy CFL's so I put mine in with my flowering ladies that were on 12/12.
Youd be better off putting them under the CFLs or getting some apporiate ones. Autoflowers like 24/0 light just about do to the fact that they grow on there own program.
This is why I didn't used to like autos,they just don't really fit my grow, I don't have a carbon filter in my veg area and it was already packed in there so the flowering tent was the best way. I was going to do an all auto run this time so it wouldn't matter but I ended up running the non-auto strains. I will probably still do an all auto run at somepoint