Rigor mortis typically sets in three to six hours after death. However, rigor mortis sets in more quickly in smaller animals than in large, so a very small dog might stiffen within a few hours.
Rigor mortis sets in several hours after death, but the time period varies depending on the size, weight, condition and heat of the dog. Cold animals set into rigor mortis more quickly, while warm animals take longer but also begin to smell sooner. After onset, rigor mortis typically lasts anywhere from eight to twelve hours, but it can last for longer or shorter periods depending on the weather and the animal.