Let me start by saying that I’m VERY picky about where I start my map. That being said, I lately have found myself click Generate New Map for half an hour at a time. During that time, I will occasionally hear the popup noise (like a merchant has come) in the background music. I’ve also noticed that sometimes my game will start during the day, and other times be start at night.
This has lead me to believe the game time starts when you click new game, not when the map is loaded.
I noticed the same passage of time during worldgen but since it’s a pretty minor and non game-breaker, I would give it a pass. I just wouldn’t agonize over where I was going to place my settlement. Still, it would be nice if it were fixed.
I will go ahead and confirm this as a bug, since it is pretty apparent it isn’t supposed to function this way. While it is probably pretty low on the list of priorities, it should be fixed when world gen/town placement gets looked at again.