According to Genesis, Noah waited seven days before the Flood began.
Genesis 7:4 records God telling Noah that in seven days He would send rain upon the earth for forty days and forty nights. Genesis 7:10 then says that after the seven days, the waters of the Flood came upon the earth. The seven-day interval is therefore the waiting period immediately before the event, not the duration of the rain.
That distinction matters because Genesis uses several different time spans in its Flood chronology. Seven days marks the interval before the waters arrive, while forty days and forty nights describes the period of rain. Other verses discuss how long the waters remained or when the Ark finally rested, creating additional numbers that are easy to combine incorrectly.
The question concerns the pre-Flood waiting period specifically. It does not ask how long Noah was in the Ark or how long rain fell. Those are separate chronological details in Genesis and should not be substituted for the seven-day interval.