I have also been able to download my pre-sale books after midnight on the release date in the past. I'm pretty sure I'm in the same timezone as Fictionwise (EDT), so it could have something to do with that. What timezone are
you in?
Once (and only once that I know of), Fictionwise offered a book for sale and had the wrong date on it, so when you tried to download it: no luck! But once they realized it, they refunded people's purchases (it had been
four months early!)
Otherwise, I'd just suggest: try again later! No fun when you want to read
now, I know.