Books like Heart of Obsidian
Nalini Singh
Heart of Obsidian is 368 pages, about 6 hours 45 minutes at 250 words a minute.
12 books to read next
How long each takes
The Guardian 7.3 h 
Dark Lycan 7.9 h 
Silence of the Wolf 6.3 h 
Nimona 5.0 h 
Oryx and Crake 7.1 h 
The Wind Through the Keyhole 6.5 h 
Pleasure 8.2 h 
Dark Lover 8.2 h 
Secret Pleasure 7.0 h 
Bone Crossed 5.8 h 
The Cloud Roads 7.2 h 
Mine to Hold 6.5 h Bar height shows length. Estimated at 250 words a minute.