TKA rehabilitation is fairly simple. Aggressive ROM in first 3 weeks (I expect to have full ROM from 0* extension -130* flexion in first month) with quadriceps strengthening and proprioception (SLS, foot setting, hurdles, tandem walks, etc). PT should last for 6 weeks post-operatively followed by patient to continue HEP afterwards.
In my clinical experience you should not wait until the knee has fibrosed to try for ROM gains. Push it early and often.