It's a bit of a gauntlet-style, dungeon run. Anyone not with the initial group would have a bit of difficulty catching up alone. Not to mention, they would miss whatever portion of the story-line the first group had already played through. Teleporting was considered, but determined it would be too much of a disruption. This all assumes the new players are all set to go with the launcher and mods. We're both pretty involved in the event as is, we won't have time to assist with set up once we begin.
As for time, we don't know. It depends on the size (and skill) of the group, really. Best guess is a couple of hours.