The Earth was flooded for about a year, including the 40 days of rain. Sediments were deposited which were later eroded, metamorphosed and lithified as the waters subsided.
The timeline for Noah's flood comes directly from scripture and this is the framework that we use to interpret evidence from the stratigraphic column.
Noah's flood was not only a world-wide catastrophe, it was also a process which involved several stages. It gives us a way to account for the stratigraphic column, Cambrian through Quaternary.