Take the example from the article:
> Please look into this for me. Do not, DO NOT, spend more than 20 minutes on this. Please come back with whatever you have after 20 minutes.
Each person looking at this is going to achieve a slightly different amount in 20 mins. Even if we ignore that, there's no guarantee that the manager making the request is going to get what they need from 20 minutes of your effort.
In 'agile' working environments, I regularly see discovery/research tasks labelled as a 'spike' and given a 'time-box'. I often question: "What happens if we don't discover what we want to in that amount of time?", and there's generally no good answer. What actually tends to happen is the 'time-box' is expanded until we found out what we needed to. So time is a terrible proxy for effort, substance, or scope. The same is true here, the manager has some idea of what they want to find out, and you better hope you can do that amount of research in their sized time-box.
I think the later examples on this article are better:
> Are you expecting something super thorough, [...] or a quick write up?
This is much more valuable because we're talking in terms of the scope of work, not how long it will take. When anyone measures in time, there's no guarantee that you'll get what you want in that amount of time, and then what? Well, we add more time!