How close to 12/12 is needed?

So I will most likely be dealing with my first photo this time around. I have both photos and autos going at the same time all under 24/7 right now.
I am thinking of what I am going to do when it comes time to flower and here is what I am wondering. Instead of having 2 sets of lights going in two different locations what if I just removed the photos from the light for 12 hours and put them somewhere pitch black with ventilation. Then 12 hours later I put them back under the light?

I am wondering how close to 12/12 would I have to be? Could I be say 13/11 and they would still flower? Also say I was 12.5/11.5 one day, 12/12 the next day, 13/11 the next day would that be a problem?

If so then that method is probably out the window and I will have to have to sets of lights going or wait till the autos are done to flip the switch.

Ok here's the thing. When it's light, it breaks down the hormone that says "FLOWER PLANTS, FLOWER!." It breaks down about the same speed as it builds up, so 18/6 it pretty much gives it no chance to flower. 13/11 or so they'd still flower but 12/12 is optimal because it actually give them full use of the hormones they produced. I actually veg til my autos are done (if I have autos) or put the autos on 12/12 for the last 2 weeks or so(it actually does finish flowering better that way imo).

im doing the same thing 24 veg for my WW and take my bagseeds out for 12 but i keep it as close to 12/12 as possible but you want to keep it under 14 hours of light to flower,i do 11/13 for like a week if im doing 18/6

Thanks for the help!!