It really varies. Recovery from ACL tears vary greatly depending on the severity of tear, if it was surgically repaired or managed with physical therapy etc. Recovery can be as short as a few weeks but can also be months as each case is unique. Exercises to strengthen the muscles around the knee are important for recovery and prevention of future injury. Results are promising with patience and a good rehab program.
6+weeks to 6+months. If you elect nonop treatment (bracing+ physical therapy), return to full activities w is 6+ wks; return to full activities after acl reconstruction surgery generally requires 6+ months and 1+ year to regain optimal function/strength; see an orthopedic sports medicine specialist to determine what is best treatment for you; sometimes in season athletes may rehab then have surgery in off season.
ACL recovery. Acl recovery is a long process. Depending on several factors, your recovery will probably require 6-9 months of activity modification. Having said that, most people can return to normal walking and standing much sooner.