The splint should extend from above the knee to below the ankle.
The general rule of splinting is:
Immobilize the bone (above and below the fracture) and immobilize the joints (above and below the...
Depends on age but should heal within appx. 2 months time maybe less, do take it easy of course and don't over exert it or kneel on it till properly healed.
if your scaphoid is fractured then just be careful to not bend your hand back or use that hand to get up. my wrist is splinted right now for a scaphoid fracture--ow!