https://infogalactic.com/info/Epiphany_season
I guess there are some modern shakeups with this in the Vatican 2 era, some of us are following the old tradition here:
Until 1955, the feast of the Epiphany in the Roman Rite of the Catholic Church had an octave, and was thus celebrated from the vigil Mass on 5 January until 13 January. After Pope Pius XII removed this octave, the liturgy of those days continued to use the same texts as previously, thus giving to the period until the Feast of the Baptism of the Lord, which replaced the Octave Day of the Epiphany, a special character
This defined the season of Christmas as extending from First Vespers of Christmas to 13 January inclusive, and divided this season into Christmastide, ending just before First Vespers of the Epiphany, and Epiphany ... from then until 13 January inclusive (one week).[11]
So Christmastide (the time after Christmas) was either defined as ending on January 5th (Epiphany), January 13th (Octave Day of Epiphany), or February 2nd (Candlemas): https://infogalactic.com/info/Christmastide
By the letter of the law, those (sedevacantists) who follow Pius XII as the last pope would then probably observe the abolished Octave of the Epiphany, but a perhaps more common approach by the spirit of the law has been to reject these changes (like the Easter week changes) as being leaning in a destructive modernist direction.
ok interesting yeah I've seen people mention things like these but for myself I've concluded that either pagan practices and Christian ones developed independently or sometimes at the same time (while being distinct), and at other times straight up Chrisitans were trying to take pagan practices and "baptize them" or remove anything non-Christian but still kind of be doing similar things.
Point is that I don't think it's just Christians being tricked in to practicing paganism as some people are concerned with, there are just too many instances of this "baptizing" of pagan practices
for example this is straight up admitted by the pope that Candlemas was a pagan adaptation, that they couldn't get rid of the practice so they just removed anything objectionable and made it into a Christian occasion:
https://infogalactic.com/info/Presentation_of_Jesus_at_the_Temple#History