Recap
Britten is visited by his Green reality self in prison to help him get where he needs to go. In order to bring down Harper he needs to join him and accept that Green is the real reality.
Britten does so, and joins up with his Green self, but not before he sees the final clue he needs to bring Harper in - the tip of her heel.
Later, as Dr. Evans is talking with Britten he "pauses" time again and creates a new reality for himself, one with both Hannah and Rex in it.