the russian sentence sounds weird too. I'd rather say something like: Во сколько завтра рассвет? or Во сколько завтра будет рассвет or even using a verb: Во сколько завтра рассветёт? It seems to me the words когда and завтра don't match well.
why is it that "when is dawn tomorrow?' accepted but not "when is the sunrise tomorrow?" or "what time is sunrise tomorrow?" the "be" doesn't seem necessary. typical DL nitpickiness. This course is very bad with consistency.