Personal preference, I guess. The more they hang, the more the muscles break down in the meat so the tenderer it is, but the taste gets more intense (gamey). Most good quality beef is hung for 21 days though. But there's a limit to how long I'd hang pheasants. The weather we've had this winter so far has been much too warm. Although we've had wind and lashings of rain, the temperature has often been in double figures, even up north. So these days, I usually do them the next day, and that's only because I'll be too knackered the day I've been out shooting.