We open presents on Christmas morning! Some years we open them right away, and others we wait until after breakfast. Both work well for us. When I was growing up, we were morning openers. My dad was responsible for maintaining the temperature in the factory he worked in so some years we had to wait until he went in and came home (and the place was probably a 30 minute drive away.) It wasn't really a long wait, but when you are little, those presents are very enticing. I remember some years my mom let us open one while he was gone, and one year we got up really early and did it, but I think all of use agreed that that didn't really work.
My favorite part of opening presents is doing it one at a time. We get to enjoy our own gifts and others' vicariously. We didn't do that when we were little, but after we adopted the tradition, I knew I would never go back!