In injury, how soon can a nose be reset if cartilage shifts off bone?

The nose can be repaired at any time after an injury to the nose. Trauma to the nose can cause a displaced, or a non displaced nasal fracture. The upper lateral cartilages could also be fractured and displaced off of the nasal bones. To repair a displaced nasal fracture, osteotomies are required  to be placed in the nasal bones.  When the upper lateral cartilages are displaced inward from trauma, a cartilaginous spreader graft is placed underneath it to put it back into its normal position.  A closed rhinoplasty approach can accomplish straightening and repairing the nose with all incisions placed on the inside of it. For many examples, please see the video and the link below

Yes the cartilage needs to be repaired as soon as possible to avoid it healing in the wrong place. Repairing cartilage within 1-2 weeks of injury is ideal. After 2-3 months it's set and becomes surrounded by scar tissue. This make surgery more difficult. However if you find a good nose surgeon with excellent reviews, this can be corrected despite its complexity. 

Dear basscleftonesAfter a fracture, the nose can be reduced to original position, ideally immediately (before swelling) or day5-7 when swelling has subsided and bones have not had a chance to heal. After that window, you generally want to wait at least 6 weeks to try and reduce the fracture, however, in my opinion, 3 months is significantly better. At 3 months or later, all components, including bone and cartilage, can be appropriately repositioned to achieve a good outcome.