This used to really bother me. But I’ve come to realize that decorating for Christmas is really more of a cultural issue than a liturgical issue. There’s no liturgical imperative to decorate (although there might be special blessings to be used for some decorations.)
The Christmas *season *runs from December 25th until the Baptism of the Lord. The Octave of Christmas runs from December 25th through January 1st. The 12 Days of Christmas go from December 25th through January 5th and are followed by the Epiphany.
In general I think it is traditional to put the tree up on Christmas Eve and keep it up through the Epiphany. ( But that’s only true for cultures that put up Christmas trees.) I’ve heard it suggested that the crib stay up until the Baptism of the Lord. (This is what my parish does.) I’ve heard others say we should wait until the Feast of the Presentation of the Lord on February 2nd. Again, this is going to be somewhat cultural.
As far as liturgical directives go… I think as long as the decorations are gone by Ash Wednesday you are OK.
Home decorating traditions are just that: traditions. In our Western culture it’s traditional to celebrate birthdays by baking a cake, putting candles on top, lighting them, singing “Happy Birthday”, making a wish, and blowing out the candles. But if someone chooses to do things differently it’s not wrong. It’s just different.