While they haven't specifically given an exact date, a talk to be given by AMD at the annual Game Developer Conference (GDC) says the following: "Join AMD Game Engineering team members for an introduction to the recently-launched AMD Ryzen CPU followed by advanced optimisation topics."

Obviously for this to be the subject of the talk Ryzen would have had to be recently launched which means that it is probably timed for that week.

GDC event runs from 27 February to 3 March and has not been put on the schedule yet and it could appear any day during the event.

AMD has not disclosed an exact date either, launching the new set of Ryzen CPUs right in the middle of both GDC and Mobile World Congress would be insane as the news would end up being buried under other GDC and smartphone announcements.
It would make sense to do it the week before all that, if not two.