Books like The Inner Citadel
Pierre Hadot
The Inner Citadel is 351 pages, about 6 hours 26 minutes at 250 words a minute.
9 books to read next
How long each takes
Meditations 3.7 h 
Freedom from the Known 2.4 h 
This I Believe 5.3 h 
Selected Works 7.8 h 
Discourses, Fragments, Handbook 7.2 h 
Better Never to Have Been 4.5 h 
Mortal Questions 4.0 h 
What I Believe 1.7 h 
The View from Nowhere 4.5 h Bar height shows length. Estimated at 250 words a minute.