If I'm paying attention, I'd say early December. But that's not the biggest problem.
Over the past several years, it seems that sending out Christmas cards at all has become a dying tradition. There probably are several reasons. The cost of postage has risen dramatically in the past decade or so. Covid probably had something to do with the decline. Maybe the ease with which we contact others by email and texting removes some of the reason for sending seasonal greetings. Anyway, the volume has declined. When that happens, the question is whether to press on or just give it up like others appear to have done.
And if the answer to that question is to adjust rather than give up, do we send only to the closest of friends? That seems logical, but one of the best things about the sending of these cards is to reconnect with valued friends and, perhaps, distant relatives that you aren't in touch with the rest of the year. So to pare down your list to the people you see or hear from regularly may be to do the opposite of the logical thing.