Take em all the way to 24/0. I've had plants take a couple months to re-veg even under that. Hit them with a shot of superthrive at a couple drops per gallon of food. The other reason plants just keep on flowering is the AGE of the cut (the from-seed age) but in your case I highly doubt that plays into it. My OGKush 'abusive' throws significant pistils under 24h light- since I store males in the same closet, I get OGK x ??? crosses making fully healthy seeds on the regular. haha ask Chron, he's about to yank some nice seeds off his OGK!
But try 24h light and superthrive.