People often bake a lot of special Christmas cookies and cakes before Christmas, and they also often do this sort of baking on more than one day. On any given day, this sort of baking might take 3 or 4 hours. And each time this sort of baking is done, it might be referred to as a 'session' or a 'round' of Christmas baking.
Yes. In the UK this takes place on the Sunday before the first Sunday of Advent - about five weeks before Christmas. (20th November 2011, most recently)
It traditionally involves your children who help you stir the ingredients to make the Christmas cakes and puddings. It is sometimes called "Stir-up" Sunday