I haven't gone to 12/12 yet they just showed their sex, as i read they may do that from time to time. Don't know the exact reasons.
But as the point of 36 hours of darkness would be to let the roots grow more and i am pretty certain that my roots are pretty well developed and there is limited space in my pots, i don't see any point in that actually. I would do it if i would put them into bigger pots tho. Dunno will see
I believe the principal reason for the extended dark period at the beginning of flowering is to get them to start flowering (and/or show sex) faster. But as you are experiencing, when you allow plants to grow to more mature plants first, nature takes care of that, lol.