After the new growth is about half grown, it will throw out some new roots. However, after the new growth is much larger, it will send out even more roots. Either time would work.
I would repot just as the new roots are about an inch long. Be careful of damaging the old roots. I turn the pot on it's side and let the plant fall away from the pot gently. I also do it dry as the moist swollen roots damage more easily. Pot it at the surface of the media not underneath.