What is the typical healing time for a compound fracture of the tibia and fibula?

Unpredictable. The healing time is very dependent on the amount of soft tissue damage that occurs at the time of the fracture. Compound fractures are those that have an opening in the skin associated with them, but it's not the opening but rather the amount of skin, tissue and bone loss as well as possible injuries to blood vessels and nerves that determines the time for healing.
6-12 weeks. Compound fractures imply an open fracture with increased risk of infection. They are a surgical emergency and need to be washed out. Because of the soft tissue injury associated with an open fracture their healing tends to take longer than a closed fracture.