Good article by my friend and fellow LCMSer Mollie Ziegler Hemingway--who, btw, was the person who introduced me to Free Republic back in November of 2000. In this article, she goes into both the religious reasons and the "fun" reasons for thinking of Christmas as the twelve-day season.
For later
In my (old) hometown of Fenton, Michigan, in the Nineteen Fifties, they had a Twelfth Night Celebration where all the Christmas trees were collected in a safe part of one of the large city parks; and under the volunteer fire brigade's watchful eye were, were burned. Right out there in the open, with the sanction of the civil authorities!
My parents told us that the practice came from an old, maybe pagan, belief that all of the evil spirits trapped in your home were burned in the event.
Our Mom was the source of that story, she had others.
For at least the past 25 years, when I hear someone on TV or radio say, “It’s the Christmas season,” during the first half of Dec., I say, “No, it’s the advent season!” I listen to Christmas songs until Jan. 5.
You obviously have been sadly misinformed as to the Liturgical Calendar.
The American Christmas Season starts immediately after the first low tide after Labor Day, and starts intensifying toward Hall'o'Ween. As the scary yard decorations come down, the very first Christmas Decorations go up, reaching a climax after Thanksgiving, when Christmas Trees appear.
The weeks between Thanksgiving and Christmas are called Insane Frenzy Time (Swahili: KWANZAAAAH!). There is a 1-week lull between Christmas and New Years for gastric recovery and rehab before the New Year's Eve Party. Once all congregants are sober, the Christmas Tree comes down and Valentine's Decorations go up, preparatory to the Easter Bunny decorating schedule.
I hope this has been helpful, as I notice you Lutherans tend to get the decorating schedule wrong.