In the seventh month, on the seventeenth day of the month, the ark rested upon the mountains of Ararat. (Genesis 8:4)Forty days. That was all. The timetable God gave to Noah was simple, but not comprehensive: for forty days... rain would fall. Nothing in Scripture indicates that God gave Noah any other information about the flood's duration.
Once the forty-first day of the flood arrived, Noah's household must have noticed two things: First, the rain had come to an end (just as God had said). Second, although the rain had come to an end, the effects of the flood had not come to an end. On the forty-first day of the flood, all that they could see out of the ark's window was... water.
Imagine thinking that after forty days, all of this is going to be over— you are going to be free to walk on solid ground again. And then, on forty-first day of the flood, you look out the window of the ark and you do not see any solid ground, but only water...
If Noah's household had been expecting that all the water would miraculously recede overnight, they must have have been terribly disappointed. On the forty-first day of the flood, Noah's household did not get to walk on solid ground. Instead, they entered the next stage of their journey at sea: the stage of uncertainty.
The Ark Comes To A Rest (Part 2) - Genesis 8:4
How God Stopped The Flood (Part 1) - Genesis 8:1-3
How Big Was Noah's Ark? - Genesis 6:15-16
The Long Expected Rain - Genesis 7:10-12