Midnight EST? Cause I just tried to apply the coupon now and it says invalid...
It's still valid and I've extended through tomorrow. The coupon is limited to the USA so if you don't enter in a zipcode for shipping estimate, it will show as invalid. Once you enter in that information you should be good to go.
Also, please note that since these are currently in use, shipment will be handled from the datacenter. Any S1 orders placed before 12 AM CST will be shipped tomorrow. Orders after the cutoff will be shipped Tuesday.