On the traditional (and current) time for eating for sangha and the 6th precept of not eating after noon, the guide is dawnrise to solar noon. So it’s relatively easy to do it with a bit of internet help to check the timings.
However, for some places on earth and some seasons, it becomes very hard, and 6 hours per 24 hours to eat is not possible by using the guide of dawnrise to solar noon. Eg. North or south pole region with 6 months of nights and 6 months of day per year, and some regions during winter time has very late sunrise.
For the late sunrise, at least if there’s enough time for one meal per day, it’s still ok.
However, for the total darkness region, then it’s better to stick to an arbitrary timing of say 6am-12pm.
Now, for the more exciting part of the discussion.
What about when (or if) humans go out to the stars or other planets of our solar system with different hours per day (defined here as time for one rotation of the planet). Or living in a space station near the asteroid belt, with only artificial lighting.
If the length of a day is similar to earth, like Mar’s about 24.5 hours per day, then it seems not much of an issue to follow the dawnrise to solar noon. If it’s a space station, usually they might follow the human bioclock and do 24 hours day and it’s the same guide as the polar regions of 6am-12pm.
Say a bit more challenging issues of 30 hours day planet, and the colonies there decided to adjust their human bioclock by just taking 30 hours as one full day. So do we still have 6 hours per 30 hours as the length of time allowed to eat, or that 1/4 of 30 hours, which is 7.5 hours to eat per day?