Is length. We’ve found anywhere from 1 day (just a picnic or something like that) to 3 days to be ideal. We did a whole week once and that was just way too much. 1 day is good for local reunions, but may not work for big reunions where people have to really travel. I know I, for one, would never spend the money on flying or drive lots of hours to just go to a picnic. But if the scale is really big, I may not want to spend 3 days with a bunch of people I don’t know, either. So pick your length carefully.