lighting question

Just wanted to see if anyone knew.MY understanding is that the plants will not go in to flower if the lights are on at least 15 hours or more a day? I am asking because i needed to tweak the lighting a bit by a couple of hours.

I go from vegging 24/7 to bloom 12/12 religously..
some use other timing methods..

I run 24/7 at the seedling stage (2 weeks after seed sprouts) and 18/6 for veg so the ladies have a little time to recover. I like to give them 24 hours of darkness right before I put them into flowering, and then I follow the 12/12 schedule until 2 days before harvest. The ladies spend their last two days in darkness before I chop them.