Spoiler: it's never done. Never. So stop asking.
The real question is: when is it good enough?
For perfectionists, "good enough" means it clears the bar you set. Anything beyond that? That's not polishing it's procrastination with a fancier name.
Don't like your definition of "good enough"? Fine, tweak it. But remember, the goal isn't perfect. The goal is to release your product into the wild before you turn into that person endlessly tweaking a draft that no one's ever going to see.