This is a very simple modification which sets the game to follow the polar day/polar night cycle. In summer the sun doesn't set at all and your sims enjoy a 24-hour sunlight period. It approaches the horizon around 1 AM and switches to the other side of the world immediately and rises again. In winter the sun doesn't rise at all and your sims umm...well...enjoy 16 hours of darkness and an 8-hour twilight. The first and last days of each season are transitional. The sun hasn't been coded to adapt its path to the changing day/night cycle, so it always follows the same path in the sky, which is a perfect arch over your sims head and the only difference is its speed. It moves slowly in the sky when a day is long but accelerates significantly when a day is short.

In spring the sun rises at 7:00 (7 AM) and sets at 19:00 (7 PM).
In summer the sun technically rises at 1:00 (1 AM) and sets at 1:00 (1 AM) the other day. It simulates polar day with a 24-hour period of sunlight.
In fall the sun rises at 6:00 (6 AM) and sets at 18:00 (6 PM).
In winter the sun technically rises and sets at noon. It simulates polar night with 16 hours of darkness and an 8-hour twilight.

As I love showing how things work, here's a video which presents the way the mod works in Lunar Lakes: CLICK HERE

This is a simple _XML modification of SeasonsManager_0xda46c4abc19a24ff. If you have a mod which modifies this file, it will conflict. Make sure there are no conflicts. Built with version 1.63.

Additional Credits:
Gurra09 for showing how to do this