From Kindle Direct Publishing:
You can make your new books available for pre-order in Kindle Stores worldwide. Setting a pre-order allows customers to order your book as early as 90 days before your book’s release date. When you make your book available for pre-order, customers can order the book anytime leading up to the release date you set and it will be delivered to them on that date.
One advantage of pre-order is that you can start promoting your book before launch to help raise awareness. You can promote your book’s pre-order page on Author Central, Goodreads, your own site, and elsewhere. Also, pre-orders will contribute toward sales rank and other Kindle Store merchandising even before your book is released, which can help more readers discover your book.
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You’ll list your book as you would with any other KDP book. When you’re adding a new book, on Step 4, “Select Your Book Release Option,” you will choose “Make my book available for pre-order” and set a date in the future. That’s it.
Though your book isn’t available for download yet, we’ll still publish a product detail page for it within 24 hours of approval. Customers can order the book anytime leading up to the release date you set and it will be delivered to them on that date. However, customers won’t be able to download sample content for pre-order books.
You can list pre-order books in all marketplaces except Amazon.com.in, where pre-orders are not currently available. Your book will release at midnight local time in each marketplace.
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When you list a book for pre-order, you’ll need to upload the final version or a draft manuscript of the book file for review. Typically, a draft manuscript would be something like a complete book that might still need copyediting and proofreading. We won’t show the version to customers, but we’ll need to preview the content for compliance with our Program Policies before creating the pre-order detail page. It will go through the same review process that any other KDP book would. Your final version must be uploaded 10 days before the release date you set.
Link to the rest at Kindle Direct Publishing and thanks to Brandilyn for the tip.