Well, I personally could abuse 5-10 minutes. And I do take timeouts at least 30 minutes, trying to maximize them to 1-2 hours. It would improve quality of the characters and decrease amounts of mass logins that everyone hate, I assume. I don't see why it would decrease 'who' - if you are playing, and have a time to keep playing, play the character you are logged in.

I'm not saying it's must be implemented, but it's just a thing to think about.