The Silver Service trains have really not had drastic scheduling changes for years. I feel that the change you describe, however, is meaningless. Since the northbound Silver Meteor, Silver Palm, Palmetto, Crescent, (and now the Carolinian on weekends), are discharge-only north of Washington, this means that they can, and often do, run ahead of schedule. As long as they arrive in Washington from the south on time, they don't have to wait for the time shown on the timetable to leave, since nobody can board. The change they showed might be the time the train was actually arriving in New York before, only now that the printed arrival time is closer to reality, they can ticket connections with an earlier train.
Of course, should the train from the south be running very late, all bets are off.