Books like Gnosticism and Early Christianity
Robert McQueen Grant
Gnosticism and Early Christianity is 241 pages, about 4 hours 25 minutes at 250 words a minute.
10 books to read next
How long each takes
The Gnostic Religion 6.6 h 
The Gnostic Gospels 3.5 h 
The Unknown Christ of Hinduism 3.6 h 
Christ and Culture 4.8 h 
The Gnostic Paul 3.3 h 
Adam, Eve, and the Serpent 3.5 h 
The Supreme Identity 3.7 h 
Christianity 21.6 h 
Transforming Mission 11.4 h 
Orthodoxy and the Religion of the Future 4.4 h Bar height shows length. Estimated at 250 words a minute.