Translation:It comes between seventeen and nineteen.
17 and 19 are not referring to times of day here. In Italian that would be "LE diciassette e LE diciannove". So they are referring to the actual numbers 17 and 19. (Other things like dates of the year or 17th and 19th position or 17-19 times would also be written differently or require extra words that are not in this sentence).
Saying "He/She comes between the number 17 and 19" doesn't make much sense. Unless you make up some convoluted interpretation, the only thing that logically comes between the number 17 and 19 is the number 18, which is an IT.
Chi viene? If DL wants the above translation should indicate what's coming. Is the package, the train, the truck coming? The students are seriously trying to learn. What is the purpose of confusing them? I admit that it is frustrating wasting time that I could use in something more productive.