Genesis 5:27

And all the days of Methuselah were nine hundred sixty and nine years: and he died.

1. Methuselah lived to be 969 years old (the oldest on record in the Bible).
2. Apparently, none of these early patriarchs lived to be 1000, suggesting that the Lord God's idea of a day, when He said Adam and Eve would die in the day they ate the forbidden fruit, was at least 1000 years.