It can take several days for an ebook to be reviewed by Apple. If accepted, you will receive an automated email from Blurb notifying you that your book is now available in the Apple iBooks Store. If your book is not approved, you will receive an automated email with Apple's reasons for rejection. You can resubmit your book after making any required adjustments.
If you resubmit a book after it has been rejected, it goes to the end of the queue, so it will take another few days to hear back again from Apple.