I have read that some people like to run veg lighting 18/6 to save electricity and to allow the plants to rest some. And some like to gradually change the lighting to mimic the natural change. Both of these methods have been repeatedly proven to not have any positive affect for the plants, and many have noted that the 18/6 schedule actually doesn't save any electricity over the length of the grow. So as the Duck said 24/0 during veg and 12/12 during flower.
I would offer, although I have not tested out fully this method, I have found that when switching to flower that turning the lights out on the plants for 24-30 hours before turning on to 12/12 caused mine to switch to flowering many days faster than just switching.
Did you do the 24hr dark run just once or several times over. I do it only once right before going to the 12/12 schedule. I put them in the dark for If I remember correctly about 26hrs then 12/12 from there. Honestly, it could be a fluke or more strain specific as my results are more anecdotal at this point.