I have a hole that is getting large and larger in the branch of my apple tree and I am wonder the best course of action to do. I've done a fair bit of reading and research, and I know most say to just do nothing. But my fear is it is going to weaken the branch and it will break soon. It i an upward facing hole, and easily collects water, which will continue the rot. I am also worried that if I trim the branch back to where the hole is located, it will make the tree unbalanced. The hole is where the blue circle is on the picture.

I posted in the tree forum and they also suggested I checked here. From my inspection, it does appear that the interior of the branch is entirely rotted.
We just purchased the property about a year ago. The tree was very over-grown and had not been properly pruned in years. We saw the knot at the time, but did not see the rot. Either the kids, or animals later dug it out,which is when we noticed the rot.

When should I cut this branch off? Should I wait till later in the fall and do it? Or do we wait till the branch brakes? I just do not want the fungus to spread to the other branch of the tree.

I will also post a few other pics.

Suggestions?
Thanks!

Lance