This was a mystery that was driving me crazy, and I’m sure I wasn’t the only one puzzled by it. But I finally found the answer by checking Amazon order receipts. The mystery being, why do some of the Amazon Kindle/digital orders close immediately, while others take half a day?
In other words, sometimes when you buy an ebook (or other digital content) you get the order confirmation email immediately, and other times you get it half a day later.