I was in a pug yesterday and we managed to complete a run in about 2.5 hours. In the end we had to kill the last boss 5 man because 1 person had to leave but it was fairly straight forward at that point because the group got to grips with the mechanics of the last boss. We even failed the last boss once because i forgot to iframe his last grab when he was on like 5%!
Our group comprised of all new players with me being the only 1 knowing the mechanics for all the bosses but only having tried the first 2 ( i read a few guides and watched some youtube videos) Plus i had to be the marker for the last boss.
I spent a lot of time explaining what to do. The first 2 bosses were pretty easy - we got them both in our second attempts. It was the last boss that took the most time.
Like someone already said it's all about trial and error but you also need to people who are willing to listen, take up roles and most importantly be patient.
In 6 man there is some room for error because someone else can always pick up a role if the other person dies. I will say that our group had 5 people with over 650+ap and it most definitely helped during some phases of the dungeon but it can easily be done with 600+ just as long as people know what they're doing.