I have had stiff fingers and wrists for quite a while. I did some small exercises in the youtube video, and they really helped.
My stiffness has resided, but how often should I keep doing these exercises?
I would add forearms rolling, since main muscles are there.
You can do that everyday, a specially when they are light, and short. I'm doing forearms rolling every 2-3 weeks - with lacrosse ball that is a bit painful. Sometimes that pain is inside the muscles, or just touching skin pains. I perform it to relax forearms and prevent elbows problems - like golfer's elbow, exercising every 2-3 weeks do the job for me.