The Death of humanity would have ended quickly but Noah still rode the through the torrential rain 40 days. Life ended in at worse 1 to 5 days but Noah had to endure the storm for 40 days before then waiting for the water to evaporate.
It's known that it wasn't the rain alone that flooded the entire earth, but that's all academic, and the Bible also says otherwise...again, academic.
Also, waiting for the water to...evaporate? Wow. You must not move about in scientific communities much...
MM