The 5th of January is the 12th night of Christmas. It is considered unlucky to leave the Christmas decorations up beyond the night of the 5th. If the decorations are still up after the 5th then superstition advises it is best to leave them up all year.

The 12th night of Christmas is Epiphany Eve. The Epiphany, on the 6th of January, is the day Christian’s record as the day Jesus Christ was revealed as God in human form. The day is also celebrated by some Christians to commemorate the Magi visiting the child Jesus.
The Epiphany has other names and other local customs. It is sometimes known as Little Christmas (or Women’s Christmas ‘Nollaig na mBan in Irish) or Dia dos Reis (Portuguese for the ‘day of the kings’). The Epiphany marks the start of the Mardi Gras season in Louisiana.
In many ways, the 12th night marks the end of the Christmas season. The Christmas decorations need to be removed in time to mark the Epiphany.
Candlemas is also a significant event in this tradition. Candlemas, also known as the Meeting of the Lord or the Feast of Presentation of Jesus at the Temple, normally occurs around the 2nd of February although some Churches will have this feast on the Sunday between the 28th of January and the 3rd of February. Once again Churches would require Christmas decorations to be down in time for the new Candlemas decorations to be put up.
It is thought by many than Candlemas is a Christianization of the Celtic festival of Imbolc. Imbolc (or Là Fhèill Brìghde in Scotland) is the day halfway between the Spring Equinox and the Winter Solstice and originally dedicated to the healing and smith-craft goddess Brigid. Imbolc is also the day the hag goddess Ceilleach gathers her firewood. Households would be ill-advised to still be decorated with greenery and while Ceilleach is out gathering.
In Pure Spirit
If you celebrate Christmas or Yule do you make sure all the decorations are down before the end of the 12th night?
No, when I was growing up we always waited until the day AFTER Jan 6, Little Christmas, to remove Christmas decorations, so as to celebrate both the American & Latin Christmas season. We decorated the Christmas tree on Christmas Eve & kept it up for the traditional 12 days of Christmas. Louisiana doesn't celebrate Mardi Gras (Fat Tuesday) until the Tuesday before Ash Wednesday which doesn't occur until February. It has nothing to do with the Feast of the Epiphany (Little Christmas) which always occurs on January 6.