I have been a runner for the last 4 years and only on rare occasions have I had any knee pain. This despite running 30 miles each week most weeks.
This does not mean that running can't be bad for the knees. A guy in my running club started running when he was in his 20s, about 35 years ago. He's still a fast runner.
But he has no cartridge left in his left knee.
He still runs. Just not as often or as fast. But he still beats me in races. He's 10 years older than I am.
What's my point?
I would say a couple things:
If you feel pain, you should probably stop walking and maybe see a health care provider about it.
If you don't feel pain, you should probably go ahead and keep walking. But there are no extra points for walking too much longer than your most recent longest walk. Don't push it too hard. Listen to what your body, especially your knees, are telling you.
Walking, in moderation, can be great for your joints. But don't walk on an injured knee. And don't over do it.