Books like The Hidden Kingdom
Tui Sutherland
The Hidden Kingdom is 336 pages, about 6 hours 10 minutes at 250 words a minute.
12 books to read next
How long each takes
The Dark Secret 5.5 h 
The Brightest Night 6.2 h 
Darkstalker 6.7 h 
The Dragonet Prophecy 5.9 h 
Moon Rising 7.1 h 
Darkness of Dragons 7.9 h 
Escaping Peril 5.7 h 
The Lost Realm 9.0 h 
The Son of Neptune 9.4 h 
The Girl of Fire and Thorns 8.0 h 
Calling on Dragons 4.5 h 
Talking to Dragons 4.7 h Bar height shows length. Estimated at 250 words a minute.