It took me nearly three years to get through them. I wasn't reading them the whole time of course, I'd put it off for months at a time, sometimes picking it up for a few paragraphs out of guilt and then putting it right back down again. There were a few chapters that I traversed in a day though, the ones I particularly remember were the chapters about the Mines of Moria, they were really compelling and the atmosphere really pulled me in (enhanced by the visuals of the film) and also the chapter(s) about Treebeard in The Two Towers, I found it oddly gripping.
Oh god but then... Lothlorien... Fucking Christ that seemed to go on for months, maybe because it took that long for me to read it... On and on and on AND I DON'T FUCKING CARE ANYMORE, especially not after such a huge climax in Moria. I remember seeing in school line graphs that visually represented a story's climax with a wave, but there's no wave there, it goes all the way up to the maximum, then there's a sheer drop down into the negatives.