Everything dates from the creation of Adam. Beyond him all is Wrapped in dark and impenetrable mystery. In order to determine the Length of time from Adam's creation to the flood we have only to add The ages of the antediluvian patriarchs--Adam, Seth, Enos, Cainan, Mahalaleel, Jared, Enoch, Methuselah, Lamech, Noah--at the births of Their first sons, and add to this the age of Shem at the flood, and we Find that it was 1656 years (Genesis 5:3-32; Genesis 7:6).

Chapter v
... there are ample indications of a more salubrious climate in the antediluvian days. ...
The emphasis lies on the chronology and on setting forth the prominent links ...
//christianbookshelf.org/leupold/exposition of genesis volume 1/chapter v.htm

The Pentateuch.
... Adam. (C.) The chronology of the book of Genesis involves, as is well known,
some difficult questions. ... manner. (1.) Antediluvian Genealogy. ...
/.../barrows/companion to the bible/chapter xix the pentateuch.htm

Chapter viii
... The chronology of the Flood is complete for all practical purposes ... of time are in
each case seven days suggests, on the one hand, that in antediluvian days time ...
/...//christianbookshelf.org/leupold/exposition of genesis volume 1/chapter viii.htm

Book 20 Footnotes
... strata under ground, till the diggers came to the antediluvian waters, with ... five
hundred years before the Christian era, according to our exactest chronology. ...
/.../josephus/the antiquities of the jews/book 20 footnotes.htm

The City of God. Index of Subjects.
... etc. Chronology, the enormously long, of heathen writers, [326]232,
[327]233; the discrepancy in that of the Hebrew and other MSS. ...
/.../augustine/on christian doctrine in four books /the city of god index.htm