Do you have a source for this eight year thing?
Hm, i’m sure i read somewhere that it would be an eight year gap between Vol.2 & Vol.3, but unfortunately i cannot find the source now.
James Gunn confirms on his twitter Account that Vol.3 takes place after Avengers 3&4:
https://twitter.com/JamesGunn/status/859481902868185088
Comingsoon.net hints in one of his articles that Vol.3 takes place years after Vol.2 (second article, scroll down): http://www.comingsoon.net/movie/guardians-of-the-galaxy-vol-3
But maybe i confused some infos due to this article, where Kevin Feige mentioned that between Vol.2 & Infinity War will be a four year gap:
http://www.cinemablend.com/news/1650709/why-the-guardians-will-be-different-when-introduced-in-avengers-infinity-war-according-to-kevin-feige
If so, i’m sorry.