transplant wen rootball has filled bottom of pot dude, if u put a small plant str8 into big pot they dont do much,,you gott make roots work 4 ya nd go looking 4 food,, thats how u get a healthy root system ,,as for flowering , it depends entirely on u m8 , wat is ur growspace / height .? u cn flower a plant at 3inches or 3m,,but u need 2 take in2 account space for slight stretching and ur buds / colas ,, u dnt wanna burn em if u run out of head room ( i had 2 learn this the hard way on 1st grow lol.) ideally u want lights about 12- 18 inch frm plant tops.(If ur using hps that is) wat system r u using ??? good luck m8y.