Janemoo is right. My brother tore his ACL last year. After having the surgery, it took 10 months for him to fully recover. Physical Therapy is a MAJOR aspect of recovery. My brother didn't attend PT as often as he should have, so 6-9 months would be a pretty good estimate.
Well, this depends on the magnitude of the injury, but you could recover from an ACL tear and meniscus repair within 6 to 9 months. After surgery, you do need to attend physical therapy sessions to strengthen the joint.