In the Beresheit account of Creation, a day begins at sundown and ends the next day at sundown. But we know closer to each of the Earth's poles, an actual day can last up to six months. The sun rises and/or sets in six month intervals. How do we reconcile this with the apparent 24-hour day in the Creation narrative?
We probably look at it as 24 hours in Jerusalem (not on the poles)
See this regarding the date line
I would imagine that you would use the Moon as Gen 1:14-19 says. Days are defined by both Sun and Moon as above verses say, precisely for cases like this.