How long do general knee sprains take to heal? I was told that the nothing isn't torn, it's only stretched. It could be my ACL or my patellar tendon

Usually 6 weeks. Ligament injury is graded by the amount of stretch or tearing and the resulting instability. Treatment varies based on injury from minimal to pt with poss brace to surgery.
Varies greatly. A sprain means a ligament (bone to bone) connector is stretched. There are four. The acl and PCL protect front to back movement of the tibia under the femur. The mcl and lcl protect side to side movement. The patella tendon (actually a ligament) connects the knee cap to the tibia. Protection from continued over stretching, ice, nsaids help but still can take weeks to months to heal in some cases.