How long does a double wrist fracture generally take to heal?

About 8 weeks... Most "wrist fractures" involve a break of both of the forearm bones at the wrist; usually only one of the two (the radius bone) is serious, however, and needs directed cast/surgery treatment. Each situation is very specific to the injury and patient and this question is important to discuss with your doctor.
Wrist fracture. This is a significant injury and can result in permanent disablity if improperly managed. Seek expert care.