Like, less than a minute.

Repetition is key, and if the text is too long, it’s not repeated enough.

To me, it’s not mind-numbing until I can “sing along” because I know it by heart. And then I move on to the next, slightly harder, text.

You don’t have to always listen to it actively, you can put it in while doing other work.

Some language self-learner books are better than others.