Question

What is your view regarding time-bound commandments in places where the daytime hours are unusually long, or do not exist at all?

Example A –
I traveled in Iceland some time ago. Dawn was around 2:00, but sunrise was only around 6:00. Is it really applicable to say that all the prohibitions before prayer (eating, traveling, and the like) already take effect from dawn, even though there is still more than an hour until even the time for tefillin?
Example B –
In places where there is sunset but no emergence of the stars, or where there is no sunset at all—do time-bound commandments apply there, and should they be fixed according to a 24-hour clock? The question of course exists in a more extreme form (and a much less practical one) in outer space, or if in the very distant future we settle other planets.
On the one hand, it is clear that when the Sages defined “the time of lying down” and “the time of rising” and matched the times for reciting the Shema to them, they did not imagine a reality in which these changes (of dawn and sunrise) do not exist.
On the other hand, it seems that at least some of their definitions rely on verses (at the beginning of tractate Berakhot they rely on “and the sun sets and he becomes pure” to say that this is the beginning of night for certain matters, or on the verse in Ezra “from dawn until the emergence of the stars” to define the day), and if so it is possible that they understood Scripture as tying the commandments to the visible state of the sky. If so, it might be impossible to fulfill time-bound commandments in such places. And I seem to remember once seeing in the name of one of the rabbis well known in the Haredi public—I do not remember which one—who said that there is a serious problem with circumcision in very far northern places during the summer and winter seasons, when there is no sunrise and sunset.