I talked to my local Apple store, and they said that if the promotion comes out within 2 weeks of the purchase date we can still get the promotion. When I asked about BTO and ordering it they said we get 2 weeks from the day it gets delivered. So I've gotten a iMac BTO on order, should be delivered on the 27, which should be right around the time of the promotion historically!
My only worry with that is if they delay the offer or something. So I'd just rather wait that little bit longer to make sure I definitely get the free iPod! Hope it all works out ok for you though!