Time is only a perception, so it is on this perception, not page count, I will answer this prompt.
The longest book I ever read was Ulysses by James Joyce. It was a "new" edition and was a required review inclusion for my column, so its heft was emphasized by time constraint. I remember that I started my review with the statement "There are two kinds of people in the literary world, those who will tell you they have read James Joyce "Ulysses" in its entirety with relish, and those who prefer truth to pretension."  I appreciated its art, its shock value and Joyce’s talent but truly felt much of the praise given to the tome reeked of  "the Emperor’s New Clothes" syndrome, right down to the intricate and intimate level Joyce’s inner neurosis were nakedly dangled in our faces. Someday I may read it again,just to see if my opinion has changed.

The shortest is tough, but recent  books that were devoured so quickly I only wished for more deliciousness and therefore had to re-read and savor again and again are James Owen’s "Here There Be Dragons", Claudia Emerson’s "late wife",  and most recently a collection called "Bordertown", in particular the final story by Charles de Lint.