The flood lasted 40 days.

"And the flood was forty days upon the earth." Genesis 7:17

The flood lasted 150 days.

"And the waters prevailed upon the earth an hundred and fifty days." Genesis 7:24

"And the waters returned from off the earth continually: and after the end of the one hundred and fifty days the waters were abated." Genesis 8:3

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Explanation:

The flood was measured by the waters from the “great deep” and the “heavens” pouring water on the surface of the earth. After 40 days, the rain and underground fountains stopped. Evaporation of this water would be very slow. It wouldn’t be until 150 days later that the water was fully dissipated, and the earth was dry. So, technically, the flood was only 40 days long, but a full evaporation of the water on earth was not until 150 days later.

"And Jacob called unto his sons, and said, Gather yourselves together, that I may tell you that which shall befall you in the last days... Dan shall judge his people, as one of the tribes of Israel. Dan shall be a serpent by the way, an adder in the path, that biteth the horse heels, so that his rider shall fall backward. I have waited for thy salvation, O LORD." Genesis 49: 1, 16-18