The scripture saying: "...one day is with the Lord as a thousand years, and a thousand years as one day." (2. Peter 3:8) is often used both by Jehovah's Witnesses and others, to show that a day can literally mean a thousand years in the eyes of God.
This is then used especially for the creation story, and for the fall of Adam and Eve. "Since one day is like a thousand years to God, it's easy to see how each creation 'day' could have been a thousand years long", they may say (at least I've heard it been said before). And also (more widely used): "Adam lived to be 930 years old after he had sinned, and this fits well with the scripture that says 'one day is like a thousand years to God', since it was said they would die on the 'day' they ate of the fruit".
Now - I've thought about this (yes, it's true, I have!).
-When I just read that scripture as-is, it simply tells me that God is 'outside of time'; time does not apply to him.
It seems though, like some people simply use their 'surgical knife' and neatly cut out half of the scripture and use it to further the thought that one 'day' is literally a thousand years (especially in Adam and Eve's case). But if it simply means that one 'day' is a thousand years in God's eyes - - why is the thought then repeated "in reverse"? Why not just say "One day is like a thousand years to God", period? I can only understand the scripture as a thought simply stating that God is not 'within time'.
Peter here semi-quoted Psalm 90:4 - that says: "For a thousand years in your sight are like a day that has just gone by, or like a watch in the night." This again reinforces to me that the intention of the writers is to say that God is "timeless", not that a thousand years is literally like one day (especially when you read the verse in context).
I also find it interesting that sometimes this scripture will be used figuratively, and sometimes to show that one day can literally mean a thousand years:
In the first case, some people (WBTS) will say that the scripture implies that the creation 'days' were undefined periods of time (they use other scriptures for this as well, but this is one of them). In other words; in this interpretation, the scripture is not 100% literal - it is used figuratively. Now suddenly each creation 'day' is not literally 1000 years, but may have been several thousands or millions of years long. In the second case, they will use the same scripture to show that the 'day' of Adam was literally a thousand years, as it fits with his age upon death.
So, in essence: - Do you need it to mean literally a thousand years? Go ahead. Do you need it to mean 'undefined period of time'? Go ahead. Twist and turn it to your liking.
I'd like some feedback to see if I've misunderstood or missed something (I'm open to saying 'Ooops - I didn't think of that!').
[edited for clarity and because 'less is more']