And WKJY (with a less-powerful signal) appears to have done it yesterday (Thanksgiving Day, November 24th). (based on Yes.com listings; I was able to go back more than 24 hours by deleting the number at the end of the address to seek a prior hour's playlist and typing-in "28" on the address bar of my web browser) WKJY flipped at 12 Noon yesterday.
Maybe someone at WALK heard about it, and WKJY's plans forced WALK to start early.
If you plan to go all-Christmas, and especially if your station is A Christmas Channel (Clear Channel) Property, and you hear that a rival may go all-Christmas before you do, you flip within a few hours, even if it's a day or two earlier than your original plans.
Maybe WALK has learned it's lesson. Publicizing the date they'd go all-Christmas was an invitation for a rival (WKJY) to try to "beat them to the punch". Fortunately from WALK's point-of-view, they were able to beat WKJY.