Most papers can be read in < 10 seconds ("not interesting, next"). Most pretty good papers can be read in 5-10 minutes. Very good papers might take a few hours. And so on.

I'm caricaturing, but only a tiny bit, this is how I read. And for good stuff, that I want to understand, a page an hour is (often) pretty typical for my first fairly thorough read.

I've written two textbooks, and in both cases I thought of the book as the distilled outcome from reading about a dozen very important papers really thoroughly