Putting an auto already flowering on 12/12?

So I've been growing 2 autos for 6 weeks now and one of them has been flowering for about 3 weeks. however the other has not auto'd at all. the one that hasn't auto'd is getting pretty big and if I don't try flower it soon then I'll have to chop it.

I've been running the whole grow on 18/6. What's gonna happen to my plant thats already flowering if I put it on 12/12? Is it gonna fuck it up by switching the lights 3 weeks into flower? What can I expect?

autos dont react well to 12/12 yield will suffer

ive heard of some buying autos that turned out to not be an auto al tll
and some autos are unstable it pays to buy for reputable breeder or seed bank

12/12 might make the none auto flower but true auto will suffer
tough call if you only have one setup

maybe put none auto outside weather is good untill auto is finished then bring it in

good luck
1Luv

Try running your autos at 20/4 instead of 18/6. I don't think that will make a difference with the not autoflowering part, but that is supposedly the best light schedule for auto's. I have been hearing alot of problems with auto's lately...