Can't say much about the duration of games.
Hi man 
Thanks for reply! - and yes, Beta will give us the answer for sure...
However, I hope you won't mind me asking you one more question...
In case online MP becomes considerably longer due to extra juice you are adding to the game via expansion(s) will you be thinking about creating extra game mode or two with different winning conditions which would focus at magic number of 30-45 minutes per round in order to save online aspect of the game?
Hard question to answer over the forums - i know... - it is just that many people out there (I personally know few dozens!) have stopped playing Sins not because game is bad but because online game is way too long...
Perhaps you were already thinking about stuff like this!?
I know that majority play SP but that majority was shaped by game design itself and not by their own choice - hell, I mainly play SP too but not because I want to but because I often haven't got more than 1hr to play a game... In some other games this would easily equal to two online rounds while in Sins I don't even log in into ICO without at least 2 hours spare...
This has been major issue for many! - trust me...
I might start a new thread with some game mode ideas 