24-hour days

Are there not twelve hours in a day? (Jn 11:9)

Young-earth creationists define the days of creation as consecutive 24-hour periods. I'm going to draw a distinction that may not change the YEC/OEC debate, but it introduces some conceptual clarity into the definition. 

It seems to me that there are basically two different ways to delineate the duration of a day. One way is to begin with the definition of a day. You define a day as the interval between the last sunrise and the next sunrise (or sunset and sunset, if you prefer). You then subdivide a day into 24 equal units of time. An hour is then 1/24 of a day. On that definition, the duration of a hour is relative to the duration of a day. An hour has no fixed duration. 

The other way is to begin with the definition of an hour. An hour has a stipulative duration. An absolute duration that's independent of the interval between the last sunrise and the next sunrise. On that definition, the duration of a day is relative to the duration of an hour (multiplied by 24).

The second definition is how modern people in a hitech civilization define a day. We use chronometers that are independent of the natural cycles of daylight and night, because that's too imprecise. We use reference frames like atomic clocks. That has nothing to do with the interval between one sunrise and the next. 

However, the first definition is how people in Bible times had to operate. In principle, that means a shorter day or longer day will have the same number of hours, since the hours are simply a fraction of a day. A shorter day means shorter hours and a longer day means longer hours, but it's the same number of hours overall. Whatever the actual duration of a day, measured by the interval between the last sunrise and the next sunrise, you divvy that up into 24 units of time. 

That distinction wouldn't make much difference to people living in the Mideast. If, however, you're living near the arctic circle, with polar days and polar nights, that makes a dramatic difference.