Geoffrey Jackson, "we just don't know"...I guess he hasn't learned the WTS trick, "the bible does not say, but" and precedes to give an answer.
Would God permit nuclear war?
The Bible does not say. It does say that “fearful sights,” or terrifying events, would occur in our day. (Luke 21:11) An example of such events includes atomic bombs being dropped during the Second World War.
How long did it take Noah to build the ark?
The Bible does not say how long it took Noah to build the ark, but it seems that he spent several decades building it. Noah was more than 500 years old when his first son was born, and he was 600 years old when the Flood occurred.b—Genesis 5:32; 7:6.
God told Noah to build the ark after his three sons were grown and married, which could have taken some 50 or 60 years. (Genesis 6:14, 18) Based on this possibility, it seems reasonable to conclude that the ark could have taken 40 or 50 years to complete.