Splitting hairs here: Do you mean that you, as user-- with LiveHeaders or equivalent-- GET a 200? Or do you mean that your site SENDS a 200?
Does the source code of the blank page have any content at all?
Blank pages generally mean there's a glitch in the php. By the time the page-building code realizes that it can't build a valid page, it has already put out some content-- even as trivial as a line break-- so it can no longer send out a 404 (or other error) header. But if so, it should still display an error page for the human user.
When it appears, the blank page loads in less than a second.
Even if the page has content at all, it can't possibly have much. So you wouldn't expect it to take time.