Books like Letters from Prison
Marquis de Sade
Letters from Prison is 401 pages, about 7 hours 21 minutes at 250 words a minute.
6 books to read next
How long each takes
The Confessions of Jean-Jacques Rousseau 11.1 h 
Correspondance 1944-1959 22.6 h 
Letters to Sartre 9.7 h 
Auguste Rodin 2.6 h 
Force of Circumstance 12.1 h 
Correspondance, 1946-1959 5.5 h Bar height shows length. Estimated at 250 words a minute.