rough guide
lets take the example of sunrise.
1.we know sunrise time at place of departure.
2.we know airborne time
3.sun travels 15 dg of lat / hour (as mentioned in previous post 5 deg in 20 min)
4.provided you are not at lattidudes too far north or too far south where there may not be a sunrise or sunset.(depending on the time of the year)
one can estimate time of crossing lattitude and thus local sunrise time based on weather you are flying east or west.
cheers