Even at the last possible moment, the door of repentance stays open. Targum Pseudo-Jonathan on (Genesis 7:4) has God tell Noah: "Behold, I give you space of seven days; if they will be converted, it shall be forgiven them; but if they will not be converted, after a time of days yet seven, I will cause rain to come down upon the earth forty days and forty nights, and will destroy all bodies of man and of beast upon the earth."
Why the extra week?
The 120 years had already been given. The ark was already built. The animals were being delivered. And still, God granted one more week.
Jewish tradition (Sanhedrin 108b) reads this as a week of mourning for Methuselah, the righteous grandfather of Noah, who died just before the Flood. Heaven held back the waters for seven days to allow proper shiva to be observed. Even the Flood waited for the mourning customs of a single righteous man.
It is also one final extension of mercy. One last week for the generation to come to its senses. They did not. The rain came. Forty days and forty nights, the world undid itself. But God had pushed the deadline to the very edge, and the Targumist is careful to let us see that the Flood, when it finally came, came only after every possible delay had been exhausted.
The takeaway is almost unbearable. The Creator of the universe will wait a week for repentance that will not come. And when at last it does not come, the rain falls.