The link in my first post says that Irans reactor, for example, could produce 30 bombs per year. Whatever that exactly means. And indicates that what is required is simply to pull the cores out early to get a good plutonium blend.
Again from the time in there you should be able to pull up to 10 bombs worth of plutonium out at once if you shut down the reactor.

So it's a matter for seperating the Uranium and other products from the weapons grade plutonium. How fast is that? I dunno. But Plutonium is a different element, not just a different isotope. So it might be easier than regular uranium refinment.