Yes. Grocery stores sell previously frozen and thawed fish with sell by dates good for 2-3 days.

Yes.
Old German expression - guests are like fish, after three days they stink.
So
1 day - you're fine.

Yes.

Earlier this evening I defrosted some fish by putting it in a ziplock and then out to f the ziplock in a bowl of warm water that I set in the counter. After it thawed, I out it in the refrigerator. Can I wait till tomorrow night to grill it?