So it's officially the end of civil twilight, you're at 40,000' wearing sunglasses, and you can log night time?
I log what I consider real night time. If I can taxi or land without lights it's day time. If I can see the instruments without needing the cockpit lights it's day time. Is any of this a sharply defined time? No.
Who's going to track down when they exactly crossed the spot on the earth that was exactly 30 minutes after the end of civil twilight? That's easy to figure out on a north/south flight, a nightmare on a east/west flight.