Here's an excert the I grabbed from medicinenet.
How long does it take to recover from a torn ACL?
Rehabilitation and return to normal function after surgical repair of an ACL tear can take six to nine months. There needs to be a balance between trying to do too much work in physical therapy returning strength and range of motion and doing too little. Being too aggressive can damage the surgical repair and cause the ligament to fail again. Too little work lengthens the time to return to normal activities.