Nice thinking! But wrong, I'm afraid. You're only assuming one line, but I did say there could be a couple of billion years' worth of lines (to be technically correct). Each and every one of those lines would be Twelve hours. Yep. It's important.
Go think about it some more, check out some other lines of thought, and let me know what you come up with.
I suppose you could also write the clue as:
Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep. Twelve hours. Yep.
...ad infinitum. Maybe that would help?