Hello, these are what I read from code:
Ananda_The_Destroyer is correct. The game cheats with NPCs.
Every day game checks if a hero gets pregnant.
First it checks if both heroes are in the same settlement. Here heroes that aren't part of player's clan have 20% chance to be considered in the same settlement even if they aren't.
Secondly, it calculates a pregnancy chance. This chance is based on couple factors:
- Number of children decreases the chance exponentially (0 child, divided by 1. 1 child, divided by 4. 2 children, divided by 9 etc).
- NPCs (including player clan) might get a penalty that depends on clan tier and clan lord count. Player doesn't get any penalty.
- The chance is decreased by female hero's age.
- The chance is increased by Virile perk
The player character with a 22 years old wife and no children has 12.4% chance without the perk.
The idea that you need to be in the same settlement during night seems to be speculation. Game checks heroes at different times of the day. Calradia is a place people can reproduce at any time