I had the same thought. I have seen several instances in DuoLingo where things are reversed from the order in which I (we) would express them. E. G. bajo o arriba So is this normal with Spanish or just this particular question composer?
temprano means early, and pronto is quickly, so I imagine the difference is pretty much what it would be in English. They can mean the same in certain situations, but generally they have a somewhat different meaning.