We open 1 gift on Christmas Eve, always pajamas. The rest of the gifts are opened on Christmas Morning as it is tradition. I love the all night anticipation, getting up early when it is still dark and opening gifts with the room lighted only by the lights of the Christmas tree.
We had an extended family Christmas one year where gifts were opened Christmas Day afternoon, after dinner, in the daylight. I was tired from cooking and lethargic from eating. There was no anticipation as my thoughts had been elsewhere and the bright day light ruined the ambiance for me.