The purpose of having characters rest periodically is to encourage players to get up and move around every so often instead of just sitting at the game non-stop. Therefore, I think we can safely say that real world time is the primary deciding factor and the character's physical fatigue is not the main issue. Also, if I understand correctly you can only sleep during the night time part of the cycle anyway, and resting is not required it only gives certain bonuses if you do. Maybe someone else knows more or knows better.

The time scale is not all reducible to the same scales in real life. One elyrian year is 4 days, each day a season. However, that doesn't mean you're going to see 184 day-night changes in one day of gameplay.

As i recall, daylight lasts something like ~3-4 hours, and night is something around ~2. Those numbers aren't perfect but they're ballparks, with night being slightly less than day.

The more you exert yourself, the more you'll depend on things like food and rest to keep your fatigue from crippling you. For a long journey across the world like you describe, you'd need to bring not just tons of food, but different kinds of outside-wear given different seasons, and something like a cot or a tent to rest in during the night cycle.

If you stay inside a "town" or a "village", you cannot die to fatigue or hunger. If you try to make an expedition and run out of food, however, you will definitely die for it and probably suffer some spirit loss.

The day night cycle is 2.5 hours with 1.5 of day and 1 of night. There's is a twilight period in between as well that is part of the 2.5 hours. You can see the info HERE.