more than likly they are root bound. quite simply they have outgrown the containers. you should get some larger pots or even 5 gallon pails and transplant them. color is good so its not a nutrient problem, just lack of space. usually when you transplant them they will start growing again in a few days or so, might take longer depending how much stress they endured but they will start to grow again.
they wont flower untill they recieve 12 hours of uninterupted darkness unless they are an autoflowering strain. they may do somthing called preflower or show sex if you will once they become sexually mature but they wont truly flower till you hit 12/12 (12 dark/ 12 light) once they are a few weeks into flowering you could go 11 dark 13 light and they will continue to flower, this is supposed to add some bud growth.
i suggest you keep them im vegitative growth for a while longer, they are small now so yield will suffer. when you do move them to flower go ahead and leave them in the dark for 24-36hrs, seems to move the flowering phase a little faster.
good luck.