That's too easy. They were activated when they began
their trip towards Earth. Activated by the sound of "All
Along the Watchtower", an Earth song. If I was the Earth's defense
system, I'd be tempted to make a dreadful pun like using "All Along the Watchtower" as a keying phrase for the true human individuals allowed past the defense barrier. These people, in my opinion, represent Earth human individuals amongst the Colonials. Where the Cylons actually fit in, I don't know – but they're close behind the fleet so maybe they have their own onboard guides.
And Starbuck's back. Of course. She looked a bit peaky though. I wonder if it's her or a copy. Or if there's any distinction between the two where she's been?
Isn't Crossroads a Cream song (pace Robert Johnson of course)? Given the lyrics, they might have used that instead of Dylan. Crossroads is creepier AND easier to dance to.