The Feast of The Epiphany (January 6th)

https://infogalactic.com/info/Epiphany_(holiday)

Epiphany (Koine Greek: Ἐπιφάνεια, Epiphaneia, "Manifestation", "striking appearance")[1] or Theophany[2] (Ancient Greek: (ἡ) Θεοφάνεια, Τheophaneia meaning "Vision of God"),[3] also known as Three Kings' Day,[4] is a Christian feast day that celebrates the revelation of God in his Son as human in Jesus Christ. In Western Christianity, the feast commemorates principally (but not solely) the visit of the Magi to the Christ child, and thus Jesus' physical manifestation to the Gentiles.[5][6] Moreover, the feast of the Epiphany ... also initiates the liturgical season of Epiphanytide.[7][8] Eastern Christians, on the other hand, commemorate the baptism of Jesus in the Jordan River, seen as his manifestation to the world as the Son of God.[9]

The traditional date for the feast is January 6.

In many Western Christian Churches, the eve of the feast is celebrated as Twelfth Night.[12][13] The Monday after Epiphany is known as Plough Monday.[14]

https://infogalactic.com/info/Plough_Monday

https://infogalactic.com/info/Twelfth_Night_(holiday)

Catholic encyclopedia on the topic of "Epiphany": https://www.newadvent.org/cathen/05504c.htm

The Irish also call today "Little Christmas": https://infogalactic.com/info/Little_Christmas

Chalking tradition:

On the Feast of the Epiphany in some parts of central Europe the priest, wearing white vestments, blesses Epiphany water, frankincense, gold, and chalk. The chalk is used to write the initials of the three magi over the doors of churches and homes. The letters stand for the initials of the Magi (traditionally named Caspar, Melchior, and Balthasar), and also the phrase Christus mansionem benedicat, which translates as "may Christ bless the house".

Chalking the door is one of the Christian Epiphanytide traditions used to bless one's home.[1]

Either on Twelfth Night (5 January), the twelfth day of Christmastide and eve of the feast of the Epiphany, or on Epiphany Day (6 January) itself, many Christians ... write on their doors or lintels with chalk in a pattern such as "20 ✝ C ✝ M ✝ B ✝ 23". The numbers in this example refer to the calendar year 2023 and the crosses to Christ. The letters C, M, and B stand for the traditional names of the Magi (Caspar, Melchior and Balthazar), or alternatively for the Latin blessing Christus mansionem benedicat ('May Christ bless this house').[2] Another form, for Three Kings day, is to mark the door with "IIIK" (the Roman numeral three followed by "K" for "Kings").

Chalking the door is done most commonly on Epiphany Day itself. However, it can be done on any day of the Epiphany season.[3] In some localities, the chalk used to write the Epiphanytide pattern is blessed by a Christian priest ... on Epiphany Day, then taken home to write the pattern.[4]

The Christian custom of chalking the door has a biblical precedent as the Israelites in the Old Testament marked their doors in order to be saved from death ... Families also perform this act to represent the hospitality of the Holy Family to the Magi (and all Gentiles); it thus serves as a house blessing to invite the presence of God in one's home.[6][a]

via Wiki

The Epiphany season extends from January 6 to Septuagesima Sunday

So, there's an octave of the Epiphany that lasts for 8 days, then there's the time after Epiphany up until Septuagesima Sunday, which is "70 days before Easter" (but not literally 70 days):

Septuagesima is the ninth Sunday before Easter, the third before Lent known among the Greeks as "Sunday of the Prodigal" from the Gospel, Luke 15, which they read on this day, called also Dominica Circumdederunt by the Latins, from the first word of the Introit of the Mass. In liturgical literature the name "Septuagesima" occurs for the first time in the Gelasian Sacramentary. Why the day (or the week, or the period) has the name Septuagesima, and the next Sunday Sexagesima, etc., is a matter of dispute among writers. It is certainly not the seventieth day before Easter, still less is the next Sunday the sixtieth, fiftieth, etc.

via Catholic encyclopedia on "Septuagesima": https://www.newadvent.org/cathen/13721b.htm

May have some further info: https://infogalactic.com/info/Epiphany_season