12/12 won't cause autos to start flowering any sooner than they normally would...they have an "internal clock" that is winding down from the moment they sprout.
Regarding your question about how to deal with autos that are sharing a space with photos that must be switched to 12/12...
Is it possible for you to move your auto seedlings (part of the day) to an area where they can get sunlight through a window or where you can at least put some fluorescent lights on them for another 6-8 hours of the day? I know the Amnesia's will do fine under 20 hours of light if you can give it to them...otherwise, they just won't grow to their full potential.
Good luck with your grow!
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