Genesis 7:10

And it came to pass after seven days, that the waters of the flood were upon the earth.

1. The flood began seven days after Noah, his family, and the animals entered the ark.
2. I suppose that living in the ark for seven days prior to the start of the flood gave everyone a chance to get used to their new surroundings and routines. It also gave them the opportunity to develop some last doubts, but apparently no one jumped ship.