Assuming the site is completely clean, the time it takes to see it indexed cleanly depends on how it takes to crawl the site at least one completely. Impossible to say.
Now if you did not do anything to clean it and it sort of seemed to get cleaned on its own I'd be extremely reluctant to say the site is clean. In fact you cannot say that at all. Things don't get fixed on their own, sites don't get unhacked by themselves. The hack must be laying dormant for now and will resurface later.