Non-native speaker here, but my partner is Swedish. From what I've picked up from him and his family, "det" is often pronounced with very little emphasis on the "t" in normal speech (it sounds more like "deh"), which can very easily be confused with "du" if you're not used to hearing it. I think you just have to get the hang of differentiating between the sound difference :)

Me too!

Same here!

Me too. Definitely sounds like du and not duh.

I would imagine not because the verb here is are, not does, and although when does it stop holds a very similar meaning, it uses, a different verb, so I would have to guess that the literal translation for that is när slutar det?

That is an accepted answer.