So far I can say that I needed around 3 hours for Wei Chapter 3-5 in NG+ (not max level) and 2.5 hours for Shu Chapter 3-5

I'd also say that the most logical way would be NG and NG+ for the three/six routes with true ending. With NG+ maybe starting in Chapter3? Also maybe leaderboards for one chapter each, even though I'm not sure if that makes sense. It's really depending on how many people actually are interested in running the game.