Those that are the Principle nomination (vacancy winner) from their congressmen and are deemed fully qualified by WP (3Qd) will hear very soon or have already been given an offer.
Those that have LOAs and are 3Qd will hear very soon if not already.
The very top people who have Presidential nominations and are 3Qd probably have an offer by now (my son got his formal offer October 14th last year for the Class of 2015)
The National Waiting List people who will get an offer will probably hear starting in January for the very top candidates but most will hear in the March time-frame. As offers are turned down on May 1 (people with offers must respond by May 1 or lose the offer) there will be additional offers to people on the NWL.