Thank you very much for your comment :)
I use the red pencil because I don't know where I put my blue... they are from the PRISMACOLOR® COL-ERASE® family.
To answer your question, I spent about four hours on it. As this is a professional job, I counted exactly how much time I spent refining my rates.
For the characters Boga and Achilles (links to the other drawings are at the top of the article) I spend between two hours and two and a half hours, and I spent three hours on the dragon Lok.