Long Afternoon

The Long Night.

Sandra Miesel interprets the Freeholder rebellion as:

"...a signal that the Empire's long afternoon was drawing to a close." (p. 132)

Thus, she unifies the current volume as much as possible. The long afternoon will be followed by the Long Night. Various peoples, including the Freeholders, plan to survive the Empire which however will still endure for generations thanks to men like Flandry. 

After the long afternoon comes "...sunset..." (ibid.) Terra and Merseia wear each other down, each devastated by internal rebellions and external attacks. At last the Long Night falls and this introduces "A Tragedy of Errors." So the book does work its way to the titular Long Night.