I've sort of pondered that question from time to time and especially lately given the Harold Camping thing about tomorrow being "Judgement Day." I personally don't believe that and think any prediction of the end will invalidate it only by what the Bible says regarding that, "no man know the day or the hour of Christ's return." Many times throughout the years I have heard people claim that, "to God a thousand years is like a day" as stated in Psalm 90:4 and reiterated in 2 Peter 3:8. Here I think we make an assumption that is not really there. It says "it is like" not plainly that "it is." I don't believe that statement was meant to be taken as an accurate scale like a year on Earth is 365 days but a year on Mercury is 88 days, so therefore, a year on Earth is like 4 years on Mercury. I think it was meant to be more of a metaphor to explain that time really has very little or no meaning to God. Yesterday and tomorrow and four thousand years from now are all viewable to God at one time. Here's more on why I feel that way.
I was curious about the "Book of Life" mentioned a few times in the Bible since the whole idea of Judgement Day has become so prevalent in recent days. There are two verses in Revelation, that, for some reason, which I was not even looking for, mention a specific time along with the "Book of Life." Revelation 17:8 says, "The beast, which you saw, once was, now is not, and yet will come up out of the Abyss and go to its destruction. The inhabitants of the earth whose names have not been written in the book of life from the creation of the world will be astonished when they see the beast, because it once was, now is not, and yet will come." What I want to point out is that statement is spoken to John, the writer of Revelation from a Heavenly being who I believe dwells outside of linear time however John, like the rest of us live in such a place that time is linear. This is why I think he speaks about the Beast in the context of human time (was, is not, will come). The thing that caught my eye was he says that there are those who's names have not been written in the Book of Life from the creation of the world. One would then assume that those whose names are written in this book have had there names in it since the dawn of time, or at least human time.
In Romans 8:29 Paul writes, "For those God foreknew he also predestined to be conformed to the image of his Son, that he might be the firstborn among many brothers and sisters." God, seeing all of human time all at one instant knew from the creation of the world, those who would freely accept him. But I'm not trying to argue Predestination verses Free Will my point is that all time is right now to God. Again, in Revelation 13:8 it says, "All inhabitants of the earth will worship the beast—all whose names have not been written in the Lamb’s book of life, the Lamb who was slain from the creation of the world." The last part of that statement is very insightful. We know Christ wasn't crucified on the first day of creation, at least not as far as linear time goes but to God it was as if it was from the dawn of time.
A strange way of looking at it is if you had a thin glass rod held out in front of you lengthwise so that you could see it was, say 5 feet long, you could look at that rod as a timeline of human history. Now, imagine you could turn that rod so that one end of it faces you. Imagine you could look down the rod all the way to the other end. In viewing it this way, all of time is technically all at one point because you can view through the entire length of the rod without moving your eye left or right. It is all right there. I think this is how God relates to time. We as humans, however; view time in terms of days, weeks, months and so on but God sees it all as now. So is a thousand man years literally equal to one day to God? I highly doubt it.
Glass image courtesy of ~love-hand-in-hand on deviantART.com