Well I just checked that CDJapan site and it says that, using the Express Mail Service, your order will be delivered within 3-6 days of shipping. So assuming they ship it the day it's released, the latest you'll get it is the day the album's released in North America. The only problem is that it's going to cost an extra $15 or so for the EMS delivery.
Have you not been able to find the digipak on any American websites? If not, I'd just get it from Amazon and not bother with the Japanese thing, unless you really want that digipak.