What about different time limits for players offline and online? For instance, when online, players get a maximum of 5-30 minutes per round, and a 1-3 days for getting online again.

What's the point? Online players take their turns when they can and do not deliberately prolong the game, even when the timelimit is set to 3 days. (Unles they are n00bs)

If you dont have them, you dont need rules...