Couple things to watch out for:
Reward points in your ACCOUNT don't expire for years (at least 5), however, once you call and have them transfer your rewards out of your account and onto your card, they expire with the card (I believe at the end of the year). Any dollars not redeemed on the card are lost.
You can transfer reward points from your account onto the card at any time - like another poster said, over the web or VIA phone. However, this does not change the expiration date of the card. If you were to transfer points to the card a day before it expires, you would have to use them that day or you would loose them.
Other than that, I believe you can use the rewards card just like a debit card to access the reward dollars you currently have on it.
We have just redeemed our points for our trip in August and the hoops didn't seem to extreme to jump through.