Timing running at 20* advance...

That's what I meant;, there's something wrong in the centrifugal; it should be over 30 centrifugal and not just 10. It seems to be malfunctioning.
At 30 it shouldn't be detonating, and if it's not, I might just leave it where it is.
But there is a very real possibility that at some time in the future, the centrifugal starts operating correctly, and them it might have 20 plus 36 =56, and that would not be good at WOT.
It's also possible that the plate is just hanging up at 20 and that if it stops doing that, then the base timing might return to it's proper place, around zero.

So in other words it's probably best to figure out the why of it and fix it as may be required.