Although the above recommendations are valuable, not everybody responds the same way.
I've had 8 knee surgeries, including a replacement. Because of all these procedures, the vascular network in my leg(s) is compromised, as are the nerves and other soft tissue structure.
After my replacement, the daktari told me that straightening my knee was more important than the bending arc. I (and the PT) worked diligently in stretching in both directions, but the bending arc was resistant to improvement. The PT took it personally, and abused my knee to the point he blew the incision open, which caused an infection, and an ugly scar. I ended up with an MUA, manipulation under anesthesia, where the daktari attempts to force the bending arc, while under general anesthesia in the surgical room. Even that didn't work, and he feared forcing it further would create more damage. The daktari agreed that we should fire the PT, and I would do my own PT at home. With all the previous surgeries, I knew what PT worked in the past. Eventually I regained my full range of motion.
My point...Not everybody is the same. Sometimes, the physical therapists can go overboard and can create additional problems. Sometimes you must listen to your own body to know what is truly right.
Because of my experience, and others, my doctor no longer prescribes PT immediately, allowing the knee to settle down somewhat after the surgery before any aggressive PT.