I think you're right that the tadpole isn't timed. I'm quite certain of that in fact. The problem is that in order to get the most out of the game the characters have to behave like it's not. We get a number of hints about it, but the problem is that based on how the game wants us to behave, the reveal you describe should come way sooner, or it should be established as near to the beginning as possible. The fact is, the process of getting camp scenes requires us to ignore the threat of the tadpole and any possibility that it's timed. And I think that means that by the time a true reveal does show up, it will be long after such a reveal would feel satisfying. It'll just be telling the player something they've already figured out.
