I do indeed note that my minor (RSI related) joint issues almost immediately disappear when I take that stuff. It seems indeed quite beneficial.
It's hard to say how long, it does take a day or 2 to kick in (when I said "immediately" I meant within a couple days when I start taking it. I probably shouldn't have used that term.)
I'm not very strict with medication so I tend to stop it when I don't have issues.
But especially in my elbows where I only have mild pain it seems to help a lot. In my wrists it doesn't as much, but I think the pain there is not totally joint-related.