I'm approaching 4 full weeks off from runner's knee. Yesterday I finally made a breakthrough. I think the key with this injury is locating the source of it. What is causing it? Once you can figure out what is causing it, like I did last night, then your recovery should be quick.
For me, I spent 3+ weeks convinced it was a weakness in my quads. So I'd do lay lifts at home and leg extension holds while sitting in my chair at work. And every 4-5 days things would feel better as a result of the rest I took. However, I'd try to run and the problem would happen again. So obviously the quad exercises were not solving anything.
Yesterday I finally got the foam roller out (long overdue) and started rolling out various areas - IT band, quads, hamstrings. And when I got to the hamstrings I could tell a noticeable difference between the left and right. And actually when I'd go over the inside of my hamstring I could feel tightness on the exact spot of where the knee had been hurting. So I spent 3-4 hours foam rolling and stretching while I watched football. And even in that time I could tell my knee was getting stronger and getting more support. I went to bed with my hamstrings feeling looser than I've ever felt in my life. Now my knee feels very close to normal.
So my point is... find the source of the problem (weak quads or tight hamstrings or tight IT Band or tight calves seem to be the common possibilities based on what I read). Rest alone seems to make things feel better, but it won't solve the problem from what I can tell.
Best of luck. It's all connected is what I'm figuring out. I think this tight hamstring of mine is what caused my plantar fasciitis for 5-6 months last year as well.