I'm trying to remember the name of a sci-fi/fantasy novel published before 1970 which is set in an abbey, where monks are engrossed in illuminated writing. Time seems to be either dark-ages or post-holocaust. There is a comment at one point about someone writing a book about what happens in the time it takes to open a window.
It's not A Canticle for Liebowitz which I just finished reading. Does anyone recognize this book?