I think 20-hour A day, not 20 hour dayS Am I right?
One man told CNN he spent six years on board one boat, and was made to work 20-hour days in life-threatening conditions.

This is CNN article's part.

I think 20-hour A day, not 20 hour dayS

Am I right?

Question

I think 20-hour A day, not 20 hour dayS  Am I right?
One man told CNN he spent six years on board one boat, and was made to work 20-hour days in life-threatening conditions.

This is CNN article's part.

I think 20-hour A day, not 20 hour dayS

Am I right?

Answer

No the article is correct, '20-hour day' is right. In this context '20-hour' is being used as an adjective. Notice the hyphen (-) connecting 20 and hour.

It's the same reason why '10-year old boy' is correct and '10-years old boy' is not.

'20 hours a day' is also correct. Notice the hyphen is not here, because here we are saying 20 hours per day.

'20-hour a day' is wrong, as is 20 hour a day.

Answer

You could say that he was made to work 20 hours a day, but the version in the article is fine too. "20-hour day" means a (work) day that's 20 hours long.