The rules state that N is either hidden, or he's not. He remains hidden until he either does something to reveal himself (leaves his hiding spot, or makes an attack, or yells out or similar) or until C takes the Search action and finds him.
Those are the rules.
As soon as N leaves his hiding spot (he cant Hide in light obscurement remember) C is assumed to notice him because (as a general rule) creatures are aware of their surroundings and when you come out of your hiding spot, the rules default to you being automatically noticed by nearby creatures.
''In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you. However, under certain circumstances, the DM might allow you to stay hidden as you approach a creature that is distracted, allowing you to gain advantage on an attack roll before you are seen.''
In our example C is not distracted. He is staring straight at N's hiding spot (a lone tree) from 30' away, and will automatically see N as soon as N leaves his hiding spot and approaches him.