By the 6th/7th of December, the sun will be setting at its earliest time in the Northern hemisphere. (Outside of the arctic circle, of course, where the sun doesn't even bother to rise!)
In another fortnight the sunset will begin getting later and later, because the EARLIEST sunset is NOT at the solstice, but a fortnight before it.
However, the sun will continue to rise LATER and LATER until a fortnight AFTER the solstice. (January 5th) the winter solstice merely marks the SHORTEST day.
So the YULTIDE season lasts from December 6th until January 5th.
Yep! Those Vikings had found the perfect excuse for a 4 week festival of debauchery. So why not join in with their uninhibited celebrations of Yule in honour of Odin and his companions in the great hall of Valhalla, without all those improbable, contrived myths of an immaculate conception (December 6th), Virgin birth (around the solstice) and tales of camel-riding wise men from the Orient following a star to a stable (January 5th).