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.