In optimal conditions, yes. But if some people are just entering the raid and learning the fights, it can take longer. Not everyone picked up the game at release and has been playing it nonstop like some of us (I've been doing that too, I'm not singling you out.) everyone was new to the raid and even this game at some point; it's the responsibility of more knowledgable players to show them the way. It is entirely possible to always run the raid the same way every time and always finish in a timely manner as you said: join a clan.