It depends on what soft tissue structure is injured.
The subcutaneuous tissues (below the skin), muscles, tendons and ligaments are all soft tissues. Tendon tears usually either require surgery or heal on their own in 6-8 weeks. Contusions (bruises) usually heal in 1-2 weeks. Most ligament sprains also heal in about 6 weeks. Of course, the severity and location play big roles in healing time.