I've had the Note 8 practically since launch, so about 1.5 years now. I'm on my 2nd phone though because I needed to have warranty replacement on my first one due to burn in, which I think was right around the 9 mo mark.
I'd definitely say that I'm largely at fault for that. Even though I had my screen timeout set to 1 minute, I generally kept my screen brightness at or near it's max with most of my usage. I have a bad habit of starting to type of an email or reply to a text and then set my phone down before finishing. This results in my on screen keyboard staying up until the screen times out. Then I'd pick the phone back up, type some more and then set it down again. All told, if I have to take a guess I'd say this happened at least 20x a day...maybe more. So that's 20 total minutes of time throughout the day that my keyboard was pulled up, but the phone was not actually in use. What was my burn in issue? The keyboard. It almost looked as if I actually had it pulled up even when I didn't.
So I dimmed the screen to around 65% with my new phone and I've done a decent job of getting into the habit of tapping the power button to power down the screen whenever I set my phone down. I've now had the replacement phone about the same amount of time as the original and I have 0 burn in to report.
Moral of the story is that while there will always be a handful of defective units out there, something like burn in is generally the result of poor ownership and bad habits.