If you expect to go on Amazon and just make a change and have it happen, don’t. It will take agonizingly long.
For example, I put up the new cover for Kiwi at around 4 am on the 23rd. and instead of the usual 12 hours they claim is the average, I finally got the notification it went live around Noon on the 24th, so let’s call that 30 hours.
But that is NOT the end of it. Amazon is not just one big system, but a monster web of systems, all interconnected, and like pushing a whale off the beach, you can’t move all of it at once. So for example, when I looked at my product listing, it still had the old cover and the old description, but the Look Inside preview showed the new cover and updated front-matter. But I can’t refresh my Kindle and get the new version yet, so I have no idea what’s going to happen when it goes up for free tomorrow through Saturday. And who knows how long it will take for embedded ads to update, if ever. (WordPress, in particular, seems to cache its own copy of the image, I discovered, with no way to force it to update).
But even worse, I deleted Kiwi from my kindle archive/library and bought it anew, and I got the old version. Oddly, my laptop mentioned it was getting an updated version, and for a good five minutes it had the new cover (in the book, but not in the library) before it too reverted to the old version, probably because of my purchase.
Oh, did I not mention? I have a Free Promo running Thursday (Christmas) through Saturday. I wasn’t going to announce it until I made the update, but now, who knows when that’s going to happen.
(Update: Amazon answered my query very quickly, reassuring me that new purchasers will have the new cover, that it may take a while for it to show up in the product description, and she manually pushed the update to my library. Apparently there is no way to force this oneself. So Kudos to Amazon support in this case.)