Looking at my own game, I spent about a week on the mechanics of the game and testing the mechanics before I even started building the first map. I literally just had a bunch of random events and a blank map to test mechanics. Then I built the game in like 3 days, lol. I did add additional content after, but yeah... I had basically all the mechanics set up ahead of time, including some mechanics I removed because I ended up not using them. It probably would've been faster if I had made the game first and then dealt with the mechanics after, lol.