When did you first suspect....(SPOILERS)

There were absolutely no clues at all. The clues given was that the events were more or less contemporary, if anything. Consider the episode, "All Along the Watchtower". Several characters inexplicably start to hear or perceive the words to the Jimi Hendrix song by the same name. That was never explained, by the way. That episode all but tells us that the events in BSG are contemporary with present day Earth. But it's a lie.

[deleted]

During the finale when they were watching the neanderthals walk across the plains. My ex-wife and I made homemade pizza and invited my Mom over. We are all big fans. I don't remember if I said it or just thought it. but it was like, "Holy shit, that's Earth! OUR Earth!"

I knew from the very beginning because that was the premise of one of the original versions of BSG. Or at least that's how I remembered it at the time.

I never suspected and I never saw any clues or indication of it until the words were mentioned at the end. Talk about a shocking surprise.

There weren't any clues, but I figured when they reached Earth, it would either be the far future or the ancient past. I say that because it'd be too difficult to pull off Earth in the present.