Laws vary by state. Always discuss postoperative activity allowances with your surgeon. Many states have basic impaired driver laws to help guide this decision. Several basic parameters can help. You should be off daytime narcotics, able to safely and efficiently enter/exit the vehicle, and your reaction times to move your foot from gas to brake pedal should be normalized. Right knee surgery will require more time.
Varies. To begin driving you should be a safe driver. This will vary from days to a few weeks. Naturally, you cannot be under the influnece of narcotic/pain meds etc. You should have good range of motion without pain and reflexes to be able to respond to a challenging situation and jam on the brakes if necessary. If your acl is done on the right knee then it could take longer. Start therapy in 1-2 weeks.