I decorate whenever I want, as much as I want, and leave it up as long as I want!
Some years it's a lot, some years it's almost nothing. Some years it goes up early, other years we're doing some slap-dash decorating on Christmas Eve. Some years it all comes down the day after Christmas, one year we only put out a single decoration and then just left it there all year long.
It depends on a lot of factors. We don't have kids, aren't religious, and we don't normally host anything for Christmas, so it's just whatever DH & I feel like doing, whenever we feel like doing it.
I used to live near a house that went all-out decorating for Halloween, and then would just add Christmas decorations to the Halloween stuff. Every. Single. Year. I thought it was hilarious - they had this big Grim Reaper skeleton that would get a Santa hat and coat and a big sack of presents. The lawn covered in tombstones would get gifts and reindeer added, and little stockings hung from each tombstone. They even had little mini Santa hats for the bats hanging from the tree.
I called it the "Christmaween" house and I loved seeing what kind of silly stuff they'd do each year. I was really bummed when they moved away! I know some of the neighbors didn't like it but I loved it. It made me laugh every time I passed by.