Penalty timers shouldn't even exist. Here's why:

1) I've been in a ton of groups that are just god-awful (undergeared, don't know their rotations, can't dodge, or just plain a-holes) and penalties force players into lose-lose situations in those types of parties (i.e. "stay here and not have any fun" or "leave and not have any fun because I'm locked out of DF).

2) Related to #1 - baddies use penalty timers to hold others hostage. They may cause numerous wipes and make a 5 min duty run out the whole timer but they'll still expect you to hold their hand and stay because DF. If you leave a duty before they get their clear, you are just "rage quitting" of course lol (um, no, not mad at all, I just value my time).

3) Penalties don't stop players from leaving. Yes, some players ask for votekicks, but that is against the rules. However, forcing a DC is not. I personally, usually do neither as I can craft/gather or just go do something else. In my case, a penalty timer doesn't dissuade me from leaving a duty at all, which makes me feel like it's pretty pointless. I'd rather spend 30 min doing something else than 30 min wiping with Baddie McGee.

4) And lastly, there are other ways of dealing with people cherry-picking dungeons if that's what you're really trying to stop. For example, have roulettes where they count on entering rather than on completion; if you enter a roulette and leave, you lose the roulette for the day. You can still play, you can still queue, get exp. or whatever. You just lose your bonus. I think that's fair. Sure, you will lose your roulette if you get DC'ed and that stinks but it's no more the end of the world than a 30 min penalty is.

TL;DR - Penalty timers don't exist to prevent players from cherry-picking roulettes so much as they exist to force players to work together. It's a really bad idea to try to force people to work together in a GAME. The world won't end without penalty timers, it will be exactly like it is right now. If you suck, others will still abandon and no penalty will ever change that.