1 day sales can largely be ignored I think. If you miss the first one wait a week or so and get another one day sale. Even so I never found them to be such good sales anyway. I call the Carnival TA and ask what are the best prices. And even later if the price goes down you can often get a reduction from the TA just with a phone call.
I always take a look if Carnival is having a one day sale. For me, the last time I was able to participate in a sale, I was able to book a balcony anywhere on the ship for the bottom balcony price. (Of course no suites!!!!)We ended up getting an 8C double aft balcony for a rock bottom price.
Sometimes it can really work for you!
CruiseDad and cruisinallthetime, this one that was posted about originally was different. It was not the typical hype. You could not use previously booked rates and have them adjusted. You could not even call in the day before and hold a cabin and finalize the next day to get the rate and other perks. This one was about better rates, half the deposit required and big onboard credits for booking on that specific date. These promos come up rarely and when they do really are a big deal.