Christmas: Do you open presents on Christmas Eve or Christmas Morning usually?

Or does it depend on when the majority can get together? How do you deal with family members who have to visit two families (theirs and in-laws) on the holiday? Do you demand that your schedule of rituals be adhered to or do you try to work something out? Or do you just let them figure it out? How about if it is you? What do you do? How do you cope with the possibility of two big meals in one afternoon?