chondromalacia

I have pretty significant chondromalacia in both knees. An orthopod has directed me to do isometrics to strengthen my quads before starting PT.
She said thirty reps, ten seconds each, TID for six months.
Question 1: I’m a big dork so I’m having a lot of trouble following this.
Is there an option to this regimen, i.e. some variation allowing doing the whole workout all at once?Question 2: Can I do vigorous walking too, or will this mess me up even more?
I’m pretty stiff afterwards. Thanks a ton.