It's fine as is. A pick up group finishing a 16-18 hour instance that requires lots of team cooperation just isn't very likely. That's not to say a pug can't do that, but it's just not likely. Not to mention it's not feasible to think that a group of strangers would stay together for a quarter of that time. If you've played an MMO with end game raiding, you understand why. Typically you can join a queue for a smaller dungeon, because the challenges aren't that hard to overcome (much like strikes). But when you get to huge end game bosses and long raids, it's not something you can queue up for; most of the time you won't even see the inside of a raid unless you're in a good guild or clan.