How fast can soft tissue stretch?

Edit Post

I am asking because I have permanently tight knees bent at 90 degree angles. Bevause of this I cannot walk.  I cannot straighten them out as the soft tissue has become shortened over time. Meaning the soft tissue adapted to this over time.

I want to know how fast soft tissue can be stretched and how much. If I can stretch it out I can finally walk again

Please tell me all you know on the matter. I really really appreciate it guys

Edit Post

Due to inactivity I sat a lot and my legs became permenently bent at the knee. I have muscular dystrophy as I couldn't exercise much so I spent much time sitting. Sitting too much caused the soft tissue to adapt and now I can't stretch my legs out and walk.

So as you can see I really would like to know information about soft tissue stretching because theoretically I can walk again as I have muscle strength but I just can't stay in my legs

Edit Post

Well the reason why I ask is because I learn that you guys have to stretch the soft tissue also after all leg lengthening which is basically what I would have to do also. I just wanted to know how much soft tissue can stretch and how fast