The night bus service only runs the nights "before" Saturday and Sunday[1]. It's a small university city with 300k population (600k greater metropolitan area).
> It's a small university city with 300k population
Made me smile, I'm from outside a city we used to call "big city" when I was growing up, it had ~110K population and is the 9th largest in the country or something :P Anyways, that city still has night service, so not sure why a city with three times the population wouldn't, especially if it's a university city.
Does Graz not have night bus service?