From Guild Wars Wiki
Enchantments last 10...20% longer
— in-game description
Upgrade components which provide this bonus
- When combined with other skills or effects that lengthen or shorten the duration of enchantments, there is no universal order in which the effects are calculated, but rather corresponds to the order in which the effects were applied to the character. Though the weapon modifier does not grant a visible effect in the effects monitor it behaves like one. Equipping or re-equipping a weapon as your active weapon set makes the weapon effect apply after other effects that were already active on the character and accordingly before effects that are applied later.