When the widest leaves reach the rim of the pot it is time to make a decision. The root system spreads out at about the same rate of growth as do the leaves. So, if the leaves are grown out the roots are too. That means the plant is ready to start vegging at an inch-a-day rate. Transplant now and the plants will go back to growing roots to fill the larger pot. Result is a taller plant that will finish later. Leave them in the smaller pots another week or 2 and you will end up with shorter, bushier plants. I prefer to top or FIM them at this point before transplanting. Good luck, BigSteve.