The magic is that the writing typically doesn't take that long. It's the digging in, researching, learning, hypothesis building, validation, etc., that may take quite a while. But that's why the documents are so powerful; once you've gone through all that (which is easier to skip, fake, or shortchange in a PowerPoint), the level of preparation and discussion is so much higher. And you likely know the answers to almost all the questions that will come up in the exec review meeting, which reduces the need for and endless series of meetings on the same topic.

So, for me, writing a 2-pager usually took 1-2 hours. After 1 week - 2 months of work getting to the point that I was ready to write. ;)

Jeff talks a lot about this in his recent letter to shareholders.

https://www.sec.gov/Archives/edgar/data/1018724/000119312518...

He suggests that a great memo takes a week or more. In my experience that's roughly right, though you'll often have been mulling over the problem for weeks before you actually start writing.