I saw the post before and was not sure how to answer it. In my case (with two 51" E8000) both, especially the second one, were clearly used (the last one had 94 hours out of the box). Now, there is one person who bought his TV on Amazon and it was advertised as used and when he checked it (after using it for at least 6 hours) he found his MRT was 12. So his used set would have had 6 hours out of the box. Another person in the UK tested his TV, fresh out of the box and his MRT was 0 which I really believe is the way it should be.
That said, 8 hours is if anything very lightly used and the key point is if there are any issues. I would check for buzzing, I would check for dead/stuck pixels and I would check for uniformity. Both of my used TVs had issues. The first one had one dead pixel and one flickering one but I could have lived with it if not for some noticeable uniformity issues, especially when running the scrolling bar. The second one also had uniformity issues, not apparent so much on the scrolling bar pattern but in full field white. This was coupled with one stuck pixel and 4 flickering ones. If you don't have any of these issues then I would keep the TV. You can definitely get worse out of the box with a set with an MRT of 0.
Edit: I was going to say check for burn-in but with 8 hours use you are not going to get burn-in, at worst, some stubborn image retention if during those 8 hours it was set to vivid or similar used as a computer monitor.