Postmoem rigidity is first apparent in the smaller muscles eg eyelids and jaw, and then it becomes evident in the remainder. Typically it is seen first in the face, then it progresses to shoulders and and finally in the large muscle groups of the limbs (Nysten's rule). In the initial 30 minutes after death there is no rigidity. Between 30min and 3 hrs after death, rigidity affects the face and eye muscles. By 6hrs rigidity affects all muscle groups and remains so for 24-36 hrs after death. From the time of 24 hr onwards rigidity stas to diminish with muscles becoming flaccid again from the time of around 36 hours. Ref: Oxford Handbook of Forensic Medicine By Tim Squires, page 33.