where does the 1 day/1000 year analysis come from???

2 Peter 3:8 (King James Version)

8But, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years as one day.

we use this to calculate many prophetic passages in the Bible.

What is God's schedule? The Bible strongly suggests that God has a total plan for the present world of 7000 years. Biblical history so far has transversed 6000 years. This history of the world consists of 3 clearly delineated periods of 2000 years each - the Early period from Adam to Abraham, the Hebrew period from Abraham to Jesus Christ, and the Christian Period from Jesus Christ to now. Add to that the 1000-year Millennium period still yet to come for a total of 7000 years. This scenario is biblically supported by:
(1) the 7-day model described in Genesis 1:1-2:3,
(2) the 7th day as a day of rest and comparing that to entering the Millennium rest (Ps 95:11, Heb 3:11, 4:3-5),
(3) the prophecy in Hosea 6:2 regarding the remaining time being 2 days plus the 3rd day, and
(4) the message in Psalm 90:3 and restated in 2Peter 3:8 that with God a day is like a 1000 years.