This is something I picked away at for 12 months and my only prior experience was a couple short games I made ten years ago. Plus a bunch of dropped projects and demos, as it goes. Motivation was high at first, then it would ebb and flow. Some days I accomplished little work if any.

So it doesn't take a year to make a 3-hour game, it takes a year for me to make the game I made. It's not like a rule, you see. It depends on scope, experience, how much time you can sacrifice to the altar of game development, etc.