I follow a bunch of authors and also specific reviewers on Amazon. Its the only way really I follow any authors so its all in one place, rather than getting a gazillion different emails from the authors individually.
I just went through my email box for some of the recent ones I got and they are all either in advance, or on the day of release. And sometimes they come a week later. Since I follow many, I also get a digest type version called "updates from who you follow", or however its called once a week or so. This is usually mostly filled with new reviews from my chosen reviewers as they review more than authors put out books.
So like today I got a notification on Amanda's new book that comes out in mid March. I got notifications from a couple of other authors with books coming out february and july. Then I got a few where it says released today and it got that on the same day as the release.
I also get other emails from amazon that are based on what I bought, borrowed. Even if I don't follow that author. I think, just based on what I see in my inbox over time, that they take in account what I read, what I buy, what I borrow via KU and library. Anything that goes through the amazon system, they take in account. Since I read everything on my kindles and most all books I read are kindle books, its easy for them to track. But I can't say I got those emails about a specific release that far behind. Its usually ahead of time for me on future releases, day of or a few days at most.