When you send off your book to Blurb, best to allow at least an hour, depending on the speed of your internet connection.
When you're ready to order in Booksmart, the book upload can take anywhere from 10 minutes to an hour or more depending on the number of images in your book. Mine was a 35MB upload for a 78 page book and only took about 10 minutes, granted this was on a fast wireless connection not being used by other people at the time.
I wouldn't recommend uploading your book on a connection slower than broadband, because it could take quite a while.
**** Update ****
If you're sending your book out after Sunday, you should be able to get UPS Second Day Air shipping for only a little extra. I ordered the Hardcover Large Format Landscape option and the UPS Ground shipping was $11, the Second Day Air was only $15.
Good luck on your book!