Gift opening is just about an all-day event for us. We try to do one at a time, and it works, for the most part. It's fine at our house, it's just the 2 DS' opening here. We go to DH's aunt's house after ours, then to the IL's, then to DH's grandma's. Considering there are 20-25 people there all day (after our house), by the time we're to grandma's....sometimes we speed it up to get done. Of course, it's usually 4:00 at least by then.
It's a great day though, all in all. DH's parents and grandma come to our house to watch our kids, we have cinammon rolls, etc. At DH's aunt's house, she always makes a huge breakfast for everyone, and we take our time eating and talking and opening gifts. At the IL's, it's usually noon or so when we get there, and we don't have real food, just appetizers and lots of cookies. Dinner is at DGrandma's, usually after the gifts are opened, sometimes before.