That's the FTL definition isn't it? Official night is 30 mins post sunset until 30 mins pre sunrise. Big difference depending which one you're talking about, especially in winter. So is most of their flying in official night or FTL night?
NIGHT as per FTL's definition will limit you max FDP (depending on the start time & number of sectors flown) while the "...± 30 mins..." is what goes in you logbook. It will fluctuate with the seasons, won't it?