temperature settings on my Electric Stove. I do not own a gas stove
Any setting on a stove is a relative estimate. The energy it puts out will have different effects on different sizes of pots and what is in it.

You should get your pot on the stove, bring it just to the boil on a higher setting, then reduce the heat a little at a time.

You will get to a setting where the broth is just barely bubbling. This is simmer, regardless of what the knob says.

And, as another comment said, monitor and add water for a 24 hour cook time.