They take 7 business days to arrive by standard shipping, which is free. I ordered mine on 3/03/04 and the card arrived on 3/12/04.
I understand that you can also get your rewards card and transfer any rewards dollars to the card from somewhere in Downtown Disney. But since you still have plenty of time to order your card, it would probably just be easier to order it to arrive at your home before your trip.
I was just about to ask this same question. Thanks for the info. Anyone know if there is a way that you can transfer your credits directly to your reservation? My fear is leaving the card at home or losing it before we arrive and I am counting on that $300 for our room.