There’s no rule for this one, so let the goal of the Big Nap determine your timing. That is, the point of not looking at a work-in-progress for a short spell is to make it possible for you to see weaknesses you’ve become blind to during your deep immersion in it. If you don’t see anything to revise after the first draft, then that’s your moment. But because first drafts usually resemble a bunch of ragged swatches duct-taped to a sewing mannequin, you’ll probably spot plenty of revision possibilities then. I’d expect the blindness to set in more commonly after the second or even third draft, when, yes, you think the story’s in good shape. That’s when fresh eyes are imperative.