Books like Cloud of Unknowing
Ira Progoff
Cloud of Unknowing is 250 pages, about 4 hours 35 minutes at 250 words a minute.
12 books to read next
How long each takes
Scivias 10.0 h 
The Ethics 4.9 h 
The Prince 2.9 h 
The Way of Perfection 5.0 h 
The Tao of Physics 6.5 h 
The Republic 7.3 h 
Mysticism 9.5 h 
Nicomachean Ethics 6.0 h 
Leviathan 9.3 h 
Letters from a Stoic 4.7 h 
Essay Concerning Human Understanding 8.2 h 
The Archaic Revival 5.3 h Bar height shows length. Estimated at 250 words a minute.