My experience is closer to 'nothers than it is Az B's. I'd recommend not riding the day of donating. You'll probably be fine, but until you've donated a time or two and know what to expect, why risk it?
Follow the eating and drinking advice and the next day go just as hard as you freaking can. Let me put it this way... you won't be setting any new max heart rates.
For me, it takes about a week before I can really put out again, and a couple of weeks to get back to full steam.