I'm interested in how long thing take to do. That seems to be very powerful information to have. We've talked about book reviews. I think 10-15 hours is about write to read the book and write and revise a book review of standard length (800 words).
A graduate level paper should take 60 minutes to read and comment on. I'll read it in 30 minutes while making some comments, and then spend another 15 minutes to write one extensive comment on the paper. If it is a very bad paper it will take longer.
I take about as much time to prepare to teach a class as to actually teach it, except for extra time to do the reading. So if the students are reading 30 pages, I have to read those pages too, then prepare in an hour for an hour length's class. If the students have to watch a movie of 90 minutes, I have to do so as well.
For a tenure case, a minute a page for the research, and then an hour a page for a three-page letter. Of course, that time doesn't include an idea that occurs to you while taking a walk during the time you are working on it, or in the middle of night.
For a pre-publication review of a book: a minute a page, then write the draft of the review in a few hours, then revise in a few more hours. I'm assuming that when I read I am thinking about what I'm reading and formulating ideas in my head, and that these ideas will take a verbal form, that I will mark places to come back to.
An article of my own can take quite a bit to write. The time it takes to accumulate the necessary knowledge is not easily conceptualized in finite terms. I was trying to understand Lorca 40 years ago.
The power of this information is to set you free. If you know how long things take then you can schedule, budget time, without either under- or overestimating time. If you are you cowed by how long something will take, you might be afraid of beginning. If you know something will take 3 hours, then you can take 1 hour on three separate days and get it done painlessly. If you think you only have 20 minutes, you might not realize that you can do one thing in that time: write 4 mails, say.