When it's today.
The traditional Roman calendar observes the Feast of the Holy Family, while the reformed Roman calendar observes either (universally, including the Diocese of Rome) the Second Sunday After Christmas, or (in the Dioceses of the USA and elsewhere) the Solemnity of the Epiphany.* Why the latter, you ask? This is a judgment by a competent territorial body of bishops, which is to say, our bishops' conference. In this instance, the term "competent" is used guardedly. You see, they think you are entirely too lazy for celebrating anything on a weekday, so they make it convenient for you. They would probably provide drive-thru confessions, only passing on the idea after ignoring the advice of an army of lawyers and "risk assessment specialists."
Should the day ever come, Deo volente, when we should succeed in converting the culture for Christ, they may be inclined to move Christmas to a Sunday as well, to coordinate our schedules with the department stores. Almost seems worth it, don't you think?
Or don't you?
We can say all we want about "the reason for the season" and "keeping Christ in Christmas" and so on. But such festivity presumes a value, a meaning, of sacred time. We can assure ourselves that "our bishops know what they're doing." But how can something be sacred if one can bend it and twist it to suit one's convenience?
And that's when you have to ask, what do they really know, about what they're doing?
Here at Chez Alexandre, we have celebrated Epiphany on the traditional day, even before -- shall we say? -- we "crossed over to the Dark Side." Still, there is a great temptation to take down the lights sometime between Christmas and New Year's Day, to put the decorations back in storage until the season returns, and to send the dying tree to its final resting place. Yet there are presents yet to wrap for the "little Christmas" twelve days after the big one.
All in good time.
* The traditional Roman calendar does allow for an "external solemnity" on the Sunday within the octave of the Feast, but that is not quite the same thing, as it does not presume a change of the Feast day itself, but merely extends that which stays as it is.