As a side question, I'm somewhat curious what this would be used for, or why it's desired? Not disagreeing with your suggestion at all, I'm more trying to picture what kind of gameplay setting would call for temporary invites. Speculating.. Is it more a case of "The first 2 players to join in the next 10 minutes can play" or is it more like, "Anyone who joins within the next month is in, if you waited longer than a month the opportunity will automatically expire." Or maybe something like "10 people get the invite this week, different 10 next week"?