How Long Does It Take to Watch Natsume's Book of Friends Season 1?

Natsume has always been an outcast because he inherited his grandmother's ability to see yokai. After moving to his grandmother's hometown and accidentally releasing a yokai imprisoned in a Lucky Cat statue, he learns about his grandmother's "Book of Friends," which contains the names of the yokai she defeated, and allows its wielder to command the yokai named within. Since then, yokai now visit him on a daily basis, seeking to either get their names back or take possession of the Book of Friends.