actually i've heard of that 30-minutes-thing during the last ten years i've been in aviation. maybe i shoud've been more precise with my question:
flying in and out of night/day, do you guys really pay exact attention to the moment when the sun finally slips behind the horizon (+30 minutes) to EXACTLY divide a sector's time between day & night?
or do you just say: heck, i'll just take one third of whole flight time i make and call it NIGHT.
or what?