I have seen people play for about 10-11 months.
In multiplayer, you need to minimize the session time as much as possible - for me, for example, it's 1-2 months. Besides, I don't want to spend more than 1-2 hours per session on the game, and it's not always possible to agree to finish the game.
PS: I've played a lot of "The Succession Wars" and the original game. I don't think the mod differs much in terms of the dynamics of development.