When the charmer is King Narciso, this is up to player choice! It will work however makes the most sense/suits the RP best for your individual character.

When the charmer is another PC, it depends on how much experience they have with the ability. Someone more practiced would be able to make their charm last longer and at more of a distance than someone new at it--but even this is within the realm of 'whatever best suits the RP' so long as player characters don't become unrealistically good at an ability too quickly. (They can be unrealistically bad at it if their players want.)