Arcana Coelestia #486
486. Verse 4 And the days of Man after he beget Seth were eight hundred years; and he beget sons and daughters.
'Days' means periods of time and states in general. 'Years' means periods of time and states in particular. 'Sons and daughters' means the truths and goods that they perceived.
Daniel 4:34
34
At the end of the days I, Nebuchadnezzar, lifted up my eyes to heaven, and my understanding returned to me, and I blessed the Most High, and I praised and honored him who lives forever; for his dominion is an everlasting dominion, and his kingdom from generation to generation.