Head injuries.
There is no single study looking at this time frame. It seems that the time frame has been accepted as a "reasonable" balance in those patients who are not getting an immediate cerebral CT.
On impact the brain shifts and strikes the rigid skull bone opposite causing damage to the brain.
The timing varies a little around the world. A player with a confirmed concussion needs to go through a graded 6 stage protocol and be cleared by a doctor before returning to play.
Cerebral Cts have improved and deliver less radiation than previously---but no---CTs use radiation by definition.
You can see the characteristic lens shape as the arterial bleed is pushing against the brain and is restricted by the skull sutures. Even though it is not on a "bone" window you can see the comminuted skull fracture.
Age is actually >65yrs. Get the MD Calc App and you can see the full inclusion and exclusion criteria. It's not perfect but still very good.
It occurs most often in babies<6mths age.
The bleed occured 10 days ago. The blood is being broken down which changes it's density and therefore it's appearance on CT. It has the characteristic curvilinear shape of a subdural haematoma which is caused by rupture of the bridging veins in the subdural space following a head injury.
Recommendations are to keep the PaC02 around 35mmHg rather then hyperventilating the patient to a lower PaC02.
A bizzare story of survival and personality change. Below is a link to one of the many articles about him.