Cicero books in order
13 books in the catalogue, about 79 hours of reading in all; the shortest takes 3 hours and the longest 9 hours.
13 standalone books in the catalogue.
Standalone books
De Officiis 4.7 h 
Catilinarians 3.0 h 
Cato Maior de Senectute 3.4 h 
Selected Works 7.8 h 
Speeches 8.9 h 
The Letters of Marcus Tullius Cicero to Several of His Friends 7.5 h 
The Letters to His Friends 7.2 h 
Tusculan Disputations 8.0 h 
Correspondence 5.4 h 
On the Commonwealth 5.1 h 
De Oratore 7.0 h 
Cicero 6.2 h 
How to Win an Argument 5.3 h