6 January Little Christmas aka Old Christmas. In Ireland, Little Christmas is also called Nollaig na mBan (in Irish) or Women's Christmas (in English).
Little Christmas article from Wikipedia     https://en.wikipedia.org/wiki/Little_Christmas
Celebration of Christmas Day on 6 January is reflected in the words of Cherry-Tree Carol, an English folk-song that migrated to Appalachia in the Eastern United States.

CHERRY TREE CAROL, Roud 453, Child 54   - Jean Ritchie       https://www.youtube.com/watch?v=nt-6me0HwgA&list=RDnt-6me0HwgA&start_radio=1 [Verse 7]
Then Joseph took Mary
All on his right knee
And said, "Tell me pretty baby
When your birthday will be"
Said, "Tell me, tell me pretty baby
When your birthday will be"

[Verse 8]
"On the sixth day of January
My birthday will be
When the stars and the elements
Doth tremble with glee
When the stars and the elements
Doth tremble with glee"

NOLLAIG NA MBAN  - Jennifer Licko      https://www.youtube.com/watch?v=WC4RXX5eYRM&list=RDWC4RXX5eYRM&start_radio=1