My advice is to not buy AC from Apple - there's a few key resellers that offer the same product at significant discounts. My small company and I have purchased about a dozen Macs, then followed with AC from other resellers. You're throwing away money if you buy AC from Apple. And, there's a little known "fact" with AC purchases too.
I've purchased AC from Adorama, B&H Photo, and Amazon after shopping around. Both Amazon Prime and B&H delivered my AC box the next day (by USPS or FedEx) at no extra charge for expedited shipping - the cost for the AC on rMBPs was $244 as opposed to Apple's $349, with B&H being in NYC (where I'm from) and my two offices are on the other side of the country in Portland and Seattle. All of the instructions were in the AC box - in less than 10 minutes I went from opening the box to having my subject rMBP's warranty extended. QED. My Mini Servers and Mac Pros are covered by way-cheaper AC sold by those parties (about a 30% discount).
The little-known fact? If one buys AC before the expiration of the standard Apple warranty, they'll honor a late registration of AC. If Apple has any questions about the purchase, they'll request a digital copy of the receipt. Adorama, B&H, and Amazon are all authorized Apple resellers. I had to verify one receipt a couple of years ago in regard to AC - I submitted a scanned copy of the receipt, and in 2 days I was covered after they contacted the reseller - so I can relate my personal experience with this point. Nice, that!