This is how we do it in Norway.

I have heard rumours that certain barbarian people in certain barbarian countries let their children run screaming and shouting out of bed, and tear open their presents early in the morning of Christmas Day. I am not one of them. In Protestant countries, people are of the opinion that Christmas presents should be opened in a calm and dignified setting -- which leaves Christmas Eve as the perfect choice. Besides, it is less rude to the children, who get to unwrap their presents more than 12 hours earlier than if we did it the Catholic way.

The foundation of the ceremony is laid already early in the afternoon, as each of the family members bring out the parcels they've hid all December, and put them under the Christmas tree. The ritual, however, doesn't begin until later, in the evening. The exact time is open for discussion in most families, except that one must never start before 17:00 (5 PM), which is regarded as the official beginning of Christmas.

The ceremony consists of two stages:

Note that it is considered slightly rude to be caught up in one's own newly opened presents when it's another one's turn to unwrap. One is supposed to have one's attention at whomever is opening his or her parcel at the moment. It is OK to sit and leaf through a book or assemble a small Lego kit, but under no circumstances should you get up from the chair and try out your new RC car before everyone is done!