They will flower regardless, you can even crank up the light hours, but its recomended you just choose a schedule and stick with it from seed to harvest, i personally go with 18/6 for the whole grow, gives the lights some rest and the plants too, both appreciate it deeply. But some strains will do best in 16/8 and some in 24/0 so pick whatever your plant enjoys the most, if she has the leaves down even before lights out, its because the plant wants less hours of light (if this is something that keeps happing daily).
Best of luck in ur grow, and pls pick my answer, its for a contest of grow questions, will help me deeply. Thanks