Taking this as valid across the board medical information when it comes from a personal injury lawyer website and ignores all the nuances of bruising behavior, types and influencing factors would be unwise.
The medical examiner testified to JO having Wischnewski spots (a type of bruising often associated with hypothermia but not exclusively) inside his stomach and pancreas only. These aren't what we know as normal soft-tissue-trauma-induced-capillary-tearing bruises. The ME cut him open and looked EVERYWHERE inside him for additional internal tissue-damage from trauma and found none outside of his skull. And CPR rib fractures. Internal injuries that bleed fill the abdominal cavity with blood. There wasn't any. We would have heard about it. Internal injuries to organs, abdominal muscles, and vessels from trauma that cause bruising would have been observed as well when she looked inside. If he had a heartbeat and time to develop raccoon eyes, and Wischnewski bruising, and bruising on his hand, common sense says she would have had time develop bruising elsewhere outside or inside from a trauma great enough to fracture the skull. The CW most assuredly would have had the ME describe in great detail any other internal or external injuries had there been any. But there weren't, so there's nothing meaningful to "wait for" with regard to deeper bruises coming to the surface from say his meaty buttocks or a bone bruise IMO. Ribs, upper pelvises, knees, ankles, acromions, scapulae elbows, hands and any other body part not padded by fat or muscle will start to show visible bruising after trauma very quickly. Seconds, minutes, not hours or days for those goose eggs and bruising to start. They'll evolve and change sometimes quite dramatically over days, but you'll see them start quickly.
The radiating skull fracture at the base of his skull occurred with such force that it created fracture lines spanning from the back of his head across his skull to the anterior (front) of his skull. He was either hit very hard, very directly, on the back of his head with a hard blunt object, or fell backwards and hit his head on something very hard. The ground wouldn't do this IMO unless he landed on a rock. Or the fire hydrant that was too far away.
He wasn't bruised enough to have been hit by a car.
MOO