One of them is behind with flowering, what do you think? why?

Just like people, all plants are different individuals. Even though your seeds came from the same packet, breeders, when they grow the seeds for you and me to buy, can hundreds of mother plants which they fertilize to make enough seeds to sell the world over. Each and every seed is an unique organic being, not a robotic item made in a factory to a set of specific standards. Every seed will have its own unique genetic composition. Even though the mother and father plants are from the same strain, seeds, like children from the same parents, will be different. You may have half of your fathers genetics and half of your mothers. So too will any of your brothers and sisters, but you are all clearly different. So too it is with seeds, all seeds are slightly different than each other. Theoretically, if you bought a 5 packet of seeds, every one of those seeds could have come from a different mother plant, but still be the same race/strain. Therefore, each seed can behave differently from other seeds, even seeds from the same plant will be different "children" plants. This is what makes breeding plants so exciting, looking for that one "extra special" seedling that is just a little different than its brothers and sisters. To have one plant flowering at different times, although they are of the same strain, is nothing unusual. You may think that one plant is flowering later than the other, however one could actually be flowering earlier than what is "normal" for that strain. So to have small differences between seedlings/plants is completely normal and nothing to be concerned over. Have you ever heard the expression "he/she is a late bloomer"? So it is with your particular plant. Hope this helps.... Organoman.