Rigor mortis is relatively brief in poultry; it is
largely complete in 4 hours in chickens (6 to 8
hours in turkeys). Rigor is not fully complete for
24 hours, but tenderness only increases marginally
after the initial 4 hours. According to Luke
Elliott, We normally advised people who bought
birds on the day of processing to wait 24 hours
before eating the bird.
Rigor is dependent on temperature: at
warmer temperatures, it occurs more quickly.
However, carcass temperature must be kept low
enough to prevent microbial growth.
I'm a proponent of aging chickens, for up to a week. (But I have also left them in the fridge for longer, and I see nothing wrong with Big Red Feather relying on the smell-test for a three week dead bird.)
I agree that rigor mortis in birds passes quickly. But it's not only about rigor mortis. If properly aged, texture and flavor improve. (Of course, that's a subjective evaluation.) The process involved is more than just letting rigor mortis pass - over time it also involves letting the muscle proteins break down. You just don't want it warm enough that bacteria multiply rapidly.
Before I got into raising DP meat birds, I was big into hunting wild pheasant, so that's my culinary starting point. Really, a 5-month-old heritage breed rooster who has been running and scratching in the weeds is not much different than a pheasant.
With pheasants, it's customary to hang them. As long as it's not too hot out, it's customary to hang deer. Beef that has been dry-aged is a delicacy and is worth considerably more than beef straight off the slaughterhouse floor. Same with lamb. The list goes on and on.
Ultimately, we all have different preferences, that's fine. But lots of people make up their mind if they like something before they give it a try.
Here's an interesting article about a guy who experimented with different aging periods for pheasant.