The system in which we read files doesn't have a timer that can measure the number of minutes a file has been open over the course of the entire season (that I know of), but there are "quick" reads and there are "long" reads. If you look at the entire application pool as a line, the quick reads would be at the extreme ends - the clear offers and the clear denies. The files that aren't at the extremes are where we spend the bulk of our time.
Here is a super complex graphic to explain.
The other factor that people don't seem to know is that we read in teams. Everyone is so used to hearing about "regional reps" in admission offices. We do specialize in certain regions (I cover much of northern Virginia and northern New Jersey), but multiple admission officers read and weigh in on an applicant's file (which is why we're always telling you to email updates to firstname.lastname@example.org and not to individual admission officers). Each application is read by at least two different officers, but can be read by as many as...well, the entire staff. How many times a file is read and how many different people read it depends on the case.
I rarely remember the files on the extremes, so sometimes a counselor will excitedly mention their star student who was admitted and I'll smile, but have no recollection of the name. I'm more likely to remember the files I read over and over again during the season as I journeyed towards a decision for them. We all write notes in the file every time we read it, but I also jot down a couple details about files I want to revisit in a notebook each year. I check up on the files a lot during the course of the review and then shred the pages when the class is full.
I'm always happy to answer questions about logistics. Feel free to post them in the comments.