Man! I didn't remember it until reading your comment, but I had the same experience in elementary school — obligatory time in the school, with access to books, but only while I was there, after finishing whatever trivial tasks were assigned.
Alas, the selection was quite lacking. So although I voraciously consumed dozens of "Hardy Boys" novels, the subsequent days were filled with irritating thoughts about how stupid they were.... perhaps the inverse of your experience.
Nevertheless, while I was trapped there, it seemed much better than nothing!
I still read books, and to me it seems obvious that most of the "experience" of reading plays out in the background in the days and weeks that follow (unfortunately, even if the book has little to offer — although as an adult I'm free to recogize that and move on to another book).
P.S.
Halfway through https://en.wikipedia.org/wiki/The_Ministry_for_the_Future and it's a good one! Much better than reading about Chet Morton's old jalopy breaking down again just as the villains are escaping on bicycles... ;-P
As a kid, at once 2 month period, I only had access to a library for a few hours on Sunday afternoons and no other time. I could not remove books.
So I read as much as I could in that time window.
5, 6, 7 books in 2 or 3 hours.
Then I'd spend the next 6 days going through them in my head and enjoying them.