David Levithan books in order
20 books in the catalogue, about 96 hours of reading in all; the shortest takes 3 hours and the longest 8 hours.
3 series and 14 standalone books in the catalogue.
Will Grayson, Will Grayson
2 books
Will Grayson, Will Grayson 6.2 h Hold Me Closer: The Tiny Cooper Story length not known
Every Day
3 books
Dash & Lily
3 books
Dash & Lily's Book of Dares 5.3 h 
The Twelve Days of Dash & Lily 4.4 h Mind the Gap, Dash & Lily length not known
Standalone books
10 Things I Hate About You 3.1 h 
Boy Meets Boy 3.8 h 
The Realm of Possibility 3.9 h 
Are We There Yet? 4.0 h 
Marly's Ghost 3.1 h 
Nick & Norah's Infinite Playlist 3.4 h 
The Full Spectrum 5.1 h 
21 Proms 5.5 h 
Naomi and Ely's No Kiss List 4.4 h 
How They Met, and Other Stories 4.7 h 
The Lover's Dictionary 4.0 h 
Every You, Every Me 4.6 h 
Two Boys Kissing 3.9 h 
My True Love Gave to Me 7.5 h