Initial Day Setting?

What effect does the initial day value have on world creation?

I’ve been using the default value of 30 coupled with a spawn delay of 2, but the last world I created I knocked the initial day back to 0 and the spawn delay to 1 to see what would happen.

Stepped out of my starting house and instead of seeing the normal low level undead, everything was in front of me…

supposedly. if you alter just the starting day (default 30) the only thing that changes is the things related to days and seasons, being that the weather and some farming, its more noticeable if you start at day between 1 and 15 on spring, food gets frozen in the morning/night, whereas in late spring it doesnt. but iirc it doesnt affect much more than that unless you rise the evolution speed and spawn rate

About being surrounded, maybe you touched the surrounded option too? or got bad luck since you changed the spawn too