I would suggest even the definition is a problem. Frankfurt, for instance, which was referenced, has very limited flights between 10 p.m. and 11 p.m. and night flights begin at 11 p.m. and end at 5 a.m., with very limited flights allowed until 6 a.m.
Would you not agree that the definition of what nighttime, that sensitive quiet sleep time for people, should be is probably not reflective of people's sleeping habits?