People should just use some common courtesy and reason in this matter. Going away for a minute or so for a quick toilet break imo is alright, but staying online while you go to dinner is simply unacceptable.
Sure it will be hard to police, but at the same time people shouldn't be so selfish as to "reserve" a slot when they want to go and do something else for over 20mins. Log off and let someone else have some fun whilst you're away - quite a few people only stay online for about half an hour anyways - and if noone else logs on after you, great! The servers a little less stressed and more stable for the rest of us.
PS: I'm so close to going into kantian ethic mode to prove how wrong this is - don't argue, just log off.