All buffs have a duration, which can be infinite (as in the case of auras). This duration is affected by Buff Duration modifiers, and can also be affected by Skill Effect Duration modifiers if the buff was applied by a skill.
The passive skills which increase buff and debuff duration apply not to buffs on you but to buffs (including debuffs) you create, either on yourself or other entities. This includes all the above as well as such things as the debuffs placed on cursed monsters.
Buff expiration – Being cursed with Temporal Chains and having the Shaper’s Presence buff can make Other effects on Cursed enemies expire % slower. These 2 mods are additive with one another and capped at 75%.