I know there's an obvious answer, but bare with me.
What I mean, is when do you consider Christmas to be upon us? IS it the first day of December where the Advent Calendars come out? The day you finish work/ school? Christmas day? Way back in May when Wal*Mart put out the decorations?
For me, it's when I see this Lorry for the first time on tele.
Associated it with Christmas since as long as I can remember. Because of my Birthday being so close to Christmas (15th) we don't put the tree or lights up until after then, but even so, this advert signals Christmas for me. What about you?