Answer:
Justin Bieber took at least 6 months to grow his fringe half the length of his forehead. Then another 2 months to grow it to the eyebrows and grow a bit of hair slightly over the ears. After that he left his hair for 3 - 4 months without cutting it and the hair will be over the eyebrows and it will cover the whole ear.
So in total it took JB the most of 11 months to a year to grow his hair.