In my experience, the cards have expired December of the next year. Any you order this year would expire December of 2013. Next year, they'd expire December of 2014. Etc.
Once you have a card, you can transfer more Rewards dollars to it (until it expires) pretty instantaneously, either on their website, or by phone. Any Rewards dollars on the card when it expires disappear. You cannot transfer them to a new card or back to your account.
Sayhello