Youre not going to notice a huge difference between ui7 and 8. Im on the beta atm
People on the forums don't really like to give estimates- 1) as we have just the same clue as you and 2) people take it to heart and kickoff later down the line
If the update were to be tomorrow when you're asleep, it'd probably take you a few days to notice. One ui 8 doesn't really have visual changes, it's all features, tweaks and deep system changes.
As johnz said, no one here has any idea for dates. So any date you see is probably pulled from thin air.