Well, I microwaved the bowl twice more yesterday and then let it sit over night and it seemed fine. No distortion that I can detect and there are no cracks that weren't a part of the blank to begin with. I've sprayed it with lacquer and here is a photo:
and here is a photo of another bowl. These two bowls were two halves of the same section of the tree branch that we harvested. Note how different the bowls are:
I may try this technique with some smaller unseasoned pieces again.
In the US today it is Memorial Day so no turning today. And a big thanks to all our service men and women, past and present, for all you do and the sacrifices you make.