I called just this past Friday and asked how long the card would be good for. I was told end of August, but if I waited until Monday it would be good until the end of Sept. I opted to wait, but I don't think I will get the card in time for our trip on the 26th. They said it's no problem and that we can pick up a temporary card at EPCOT service window. We have done this once b4. It's a slight pain, but it's worth it in case we want to go sometime next Sept., we have a "free" month.
Just keep in mind when and if you call to order, you can ask them how long it will be good for and if you waited, when it would change to the end of the following month.