John Gill Commentary Genesis 7:17

"And the flood was forty days upon the earth; and the waters increased, and bare up the ark, and it was lifted up above the earth." — Genesis 7:17 (ASV)

And the flood was forty days upon the earth This is said with respect to what follows, and the meaning is, that when and after the flood had been upon the earth so long, then the waters increased, and bore up the ark, and it was lift up above the earth; after this they were so many and so strong that they lifted up the ark from the place where it stood, and bore it up, that it touched not the earth; and Aben Ezra from this infers, that the ark did not remove from its place after the flood began, until forty days.