Serena Valentino books in order
12 books in the catalogue, about 64 hours of reading in all; the shortest takes 4 hours and the longest 12 hours.
1 series and 11 standalone books in the catalogue.
GloomCookie
5 books
GloomCookie 4.1 h GloomCookie, Volume 2 length not known
Broken Curses length not known
The Carnival Wars length not known
The Final Curtain length not known
Standalone books
Fairest of All (2 editions) 4.6 h 
The Beast Within 4.0 h 
Poor Unfortunate Soul 3.8 h 
Fairest of All: A Tale of the Wicked Queen 5.0 h Mistress of All Evil (2 editions) 5.7 h 
Serena Valentino's Villains Box Set: Books 1-3 11.7 h 
Mother Knows Best 5.6 h 
The Odd Sisters 5.2 h 
Evil Thing 4.4 h Cold Hearted 5.6 h Never Never 4.7 h