This is a personal decision, one that can only arise from your own interest in the work. It would be easier, wouldn’t it, if we had assurance that once you hit, say, 432 hours of revision, you’ve done all you can? That’s just not the case, though, so the decision is up to you.
If you’re still engaged in the piece and eager to strengthen it, then continue revising. Be aware of how you’re revising. If you’re tinkering with language, even though you know the plot needs a major overhaul, you might consider how you can better focus your efforts. If you’re taking it apart in a more genuine and productive way, forge ahead.
However, if you’re not still engaged with the story, perhaps it is time to put it…