Chris Riddell books in order
20 books in the catalogue, about 108 hours of reading in all; the shortest takes 1 hour and the longest 14 hours.
1 series and 18 standalone books in the catalogue.
Ottoline
4 books
Ottoline and the Yellow Cat 3.2 h 
Ottoline Goes to School 3.2 h Ottoline at Sea length not known
Ottoline and the Purple Fox length not known
Standalone books
Just William 4.1 h 
Stormchaser 7.3 h 
The Schoolmouse 2.4 h 
Beyond the Deepwoods 5.3 h 
Castle Diary 1.2 h 
Fortunately, the Milk 2.4 h 
Midnight Over Sanctaphrax 6.8 h 
Pirate Diary Journal of Jake Carpenter 1.2 h 
The Curse of the Gloamglozer 7.0 h 
The Last of the Sky Pirates 7.0 h 
Vox, Edge Chronicles Book 6 7.3 h 
Freeglader 7.5 h 
The Winter Knights 7.0 h 
Clash of the Sky Galleons 7.8 h 
The Lost Barkscrolls 7.3 h 
The Immortals 13.6 h 
Goth Girl and the Ghost Mouse 4.1 h 
Art Matters 2.3 h