Maybe it's just me being an American who celebrates Christmas, but I try to wait on breaking out the Christmas music, decorations, and gifts (although I might buy them before) until after Thanksgiving. It's hard to do when Nov. 1 means red and green all over the stores these days.
I think when I've participated before I mailed by or around the first of December.
It may be worth noting that Hanukkah is Dec. 1-9 this year, however.