I would recommend waiting a few months. You want to distance yourself from the narrative long enough to forget about it. That way, when you come back to it later, you're looking at it with fresh eyes and can find more mistakes. Other than that, it also gives you a renewed sense of drive. After writing something new, it's easy to get sick of it and not want to deal with it, but after a few months away, you'll be eager and happy to jump back in. I used to write my novel primarily during the summer (not during the school year) so each time I came back it was refreshing and I got a lot more done.