0 used to mean a time when you do not know exactly what it is or when it is not important what it is -- いつか, そのうちに
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
道路がどれだけ長くても、一歩一歩完了することができますし、足跡をマークしなければ、道路がどんなに短くても完了することはできません。