Twelfth Night is not the same as Epiphany. Twelfth Night is the night before Epiphany. Twelfth Night is 5th January and Epiphany is 6th January.
OrinocoDugong, I agree with most of this:
It's more a symptom that there are two festivals celebrated at this time of year. One is entirely secular and is celebrated from mid-November to 26th December. The other is religious and is celebrated from 24th December to 6th January.
However, we're not religious and we stick to the twelve days model. One reason is we have a family birthday in the middle of December and we like to celebrate that properly so we don't do anything for Christmas till after that.
Advent means very little to me - we don't even have an Advent calendar. We have a very pared down Christmas, so no mad rush to get everything ready (no children around either), and as it happens none of us are back to work till early January, so that helps.
I think of Christmas as a midwinter festival, as a way of making this dark, miserable season more enjoyable. Makes perfect sense that in the Northern Hemisphere before the days of cheap, effective lighting people could get very little work done, so did what they absolutely had to, and spent the rest of the time making the best of things by having a feast and a break before the longer days arrive in the New Year.
The Romans called it Saturnalia, the Jews have Hanukkah, the Hindus (a bit earlier) have Diwali, the Vikings had Yule, Christians (and now most of the world, in secular form) have Christmas. Starts with the Solstice, ends a few days later at the point when it is clearly getting lighter in the mornings.