I’ve always wondered about this, so I went online to see if there are any actual “guidelines” on this subject.
“Every family moves at their own pace when it comes to taking down Christmas trees and decorations, but there are certain popular dates to remember that are approaching when people will start taking them down. Those specific dates follow either religious or even just superstitious guidelines.” SOURCE
Superstitions would have you take the tree down and UNdecorate before midnight on the last day of the year so not to drag old baggage and bad luck into the New Year.
Tradition considers THIS to be the 12th day of Christmas—the last day of all the Christmas celebrations and merriment.
Taking down the tree on this day is usually in observance of the Epiphany, or Three Kings Day (a Christian holiday).
Now, at the other end of this query lie the folks that take it down and to the curb –Christmas night– yikes!
I admit that -for me- it can be the end of January
before I start UNdecorating!