I interviewed on 10/8. They told me their turn around time was 4-6 weeks, but not to call until your 6th week. I heard from them on 11/9 and my letter was dated the 1st. Hope that helps.
I remember the dean discouraging us from calling them too often...I think it might be good to wait til 6 weeks has passed. Also, the turnaround time is likely to be longer now than in October, when they were just starting to interview. good luck!