"Exact time may vary." They have to give a cut off date that refunds will be given and it can't be after release but that doesn't mean it will be right before release either. 3rd week of April is when many people believe it will be released. Kripparrian, after visiting Blizzard EU, even says that the encounter he played needed a little work so April 15th is a pretty decent guess.
If this is accurate, the pre-order will be ending soon, and no more card back. I doubt it is accurate though. I'm certain there will be an announcement at least a week prior to release.