As an exercise I did a rough analysis of the arrangement of Genesis 1-11 in respect of the occurance of date information.
Others might like to analyse this further, to see if it leads anywhere in particular, but I found that about 19% of verses in Genesis 1 are concerned with dating the action reported, and again about 19% of verses in Genesis 1-11 have the same concern, with a couple of major groupings as though they were calibrations of the timing of action.
See the diagram I prepared.
