Charms fill up by gaining charges in different ways, the first buff improves that

when a Charm activities it starts a buff that has a duration, that’s what the second buff improves

the choice is… Charms more often? or charm for longer

Charm duration is generally better if you would run charms that aren’t what I call the “oh shit” charms, meaning charms that apply a generally useful buff like the gold charm or any of the flat ele res charms (why you’d use those idk).

Charms charges is better for your “oh shit” charms, those being freeze immune, stun immune, and the like, as its much less likely that you’d be frozen repeatedly in a short time span and that means its better if it can proc more often rather than for longer.