I dont think meeting times would be much to worry about. I imagine that most people will only want to play a 1v1 campaign with their close friends as you can`t garuantee that a random player will ever show up again after the first session. I`ve said it before in another thread so I apologise if I appear to be repeating myself, but the best solution to making sure one player isn`t simply waiting around is to have him/her control the AI armies in battle. Any MP campaign where all battles would be automatically calculated seems totally pointless to me.