Why After 7 Days did the Flood Waters fall

I now understand the meaning...... “10And after seven days the floodwaters came upon the earth. 11In the six hundredth year of Noah’s life, on the seventeenth day of the second month, all the fountains of the great deep burst forth, and the floodgates of the heavens were opened. 12And the rain fell upon the earth for forty days and forty nights.“