The most Latin I've read has been Genesis, chapter 24, which weighs in at 7552 characters, or two printed pages in my edition. The most classical Latin I've consumed in one day would be one of Pliny's letters to Trajan.
It took me several hours, and I didn't understand all of it, even with the copious notes in Wheelock's reader, but I did find it fascinating commentary on early Christianity ;p
For comparison, in English, I read all of Chuck Yeager's autobiography
in one day. Actually, it took me a little longer than a day, 26 hours, to read all 446 pages of it. I've also read both Genesis and Exodus in one day using the translation at www.netbible.com