I always have mine gutted within the hour. You could wait a little longer, we shoot pheasants and carry them for 3-4 hours in the truck etc. before cleaning them. Sooner is better. I sanitize mine with a couple tablespoons of bleach in a five gallon pail before rinsing and freezing them...
This is probably from Cardiac arrythmia (irregular Heartbeat) that is a common problem with this breed. They also develop congestive heart failure at an older age. These problems can be largely mitigated by slowing their growth. Taking away the feed as they get older for 8-10 hours at night...