I just tried to order Hawk and a Viper using a $15 off code and it says "Our records show that this code expired on 2012-01-05."
Ummm... that's today. WTF?
It has to do with the time. I forgot what time they go by (I think Prime Meridian), but the same thing happened to me last year with a comicon 100.00 gift card. I waited to the last day, and when I tried it that evening it was expired, even though it expiration date was that day and I live in California. Go figure.