Note: This can only be done after the task that involves helping Colin at the Owlery. Climb up the pole next to the stairs that the Devil's Snare blocked before. Maneuver along the wall until you reach the first window, then jump inside. Ron and Hermione are not there. They are still outside watching you, but when you exit the Owlery, they will come out of the door directly behind you and are no longer standing by the pole.