Ive had keyhole surgery on torn cartilages in both knees, each time only needing a week off work. All depends on how strong your leg muscles are prior to surgery. Once the initial swelling has gone (a few days) it shouldnt be too bad, but dont force any bending of the knee as you dont want re inflame it. I went for a 7 mile run two weeks after the first op, three nights on the go. Ended up re inflaming it and had further problems for 11 months after, although I still managed to work. The secong op, I was working after a week, walking the 3 Peaks after two weeks, but didnt run for 5 months, and have had no further problems in the 5 years since.
Dave.