As far as the three kings is concerned it is not christmas as such, but the Epiphany and the celebration that represents the end of Christmas. Christmas is still on the 25th and I would almost certainly look for a reservation for that night.Many Restaurants do not open but hotels do tend to serve Christmas meals. I don't know the options you may have where ever you are going, but on New Years Eve most restaurants are open around the country and serve up special menus etc.