Nowadays that is when you take the tree and decs down. Times change.
Back in the day, the bleak mid winter was really bleak. The twelve days of Christmas was quite a thing, when not much else could happen in a largely agrarian society. Each day had a name and a meaning and customs which might be followed. At last one involved a Roman style saturnalian role reversal - the lord became the servant and the servant the master. How much of all that stuff would be performed probably varied from area to area, just as modern xmas customs do today (bah humbug)
Nowadays wassailing is all that's left of an old custom and an old way of saying cheers and perhaps also the old English equivalent of the Italian "ciao".
Was hal!