Books like Portable Darkness
Aleister Crowley, Robert Anton Wilson
Portable Darkness is 320 pages, about 5 hours 52 minutes at 250 words a minute.
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More Simplified Magic 8.2 h 
Wheels of Life 9.4 h 
The Key of Solomon the King 2.7 h 
On Monsters 6.8 h 
Thinner 5.8 h 
Taltos 8.9 h 
Heaven and Earth 7.0 h Bar height shows length. Estimated at 250 words a minute.