According to Genesis, Noah waited seven days before the Flood began after receiving the final warning to enter the Ark. Genesis 7:4 says that God announced seven days would pass before the rain came for 40 days and 40 nights.
Genesis 7:10 then states that after the seven days, the waters of the Flood came upon the earth. This seven-day interval is separate from the 40-day period of rain and from the much longer chronology of the waters rising and receding.
The passage gives the interval as a final preparation period for Noah, his household, and the animals. It does not identify the seven days as the time required to build the Ark; construction is described earlier, with no complete building duration supplied.
Readers sometimes merge the seven-day warning with the 40 days of rain, but Genesis presents them as two distinct periods in sequence.