December. Putting them up in November is just weird, it's not even Advent yet, never mind Christmas!
Also I don't get this trend of putting decorations up in like November, but then taking them down on boxing day. Christmas is twelve days, people! It's from December 25th to January 6th. That's why the song is "the twelve days of Christmas". We're meant to get twelve days off work, but corporate capitalist rubbish has pushed the "Christmas shopping" part to start as early as November, while sweeping the "holiday where you hang out with friends and family and rest" part under the rug and encouraging people to take their decorations down and go back to work before it's even new year's, because I guess they like the part where people buy things, but hate the part where people get time off work... 
I put my decos up in mid-late December, then I take them down on Twelfth Night (Jan 6th) (Also my favourite Shakespeare Play).