Concept of game length

SO in concept of two rules

If u die u start at the beginning, U have to complete the dungeon to save OR find a save point(they will be scarce), HOW long should a battle and dungeon route last? Or in your opinions?

DUE TO game lenghts can vary person by person, and i know everyone has a fav for types, but again dependent by games, so in your opppinion WHAT is a good game lengh for a single dungeon run?