- Not available on that edition (the reason is in the tooltip)
- Depends on the setting, your class or another addon (details in the tooltip)
What it does
Checks how much time is left on the debuff you choose on the unit specified, compared with the number of seconds you set. An absent debuff does not match, and a permanent debuff counts as never running out.
Why you might use it
Compares the time left on a debuff, so you can refresh it before it falls off. Typical steps are renewing Sunder Armor, Flame Shock or Rip with a few seconds left, or reapplying your own damage over time effect just before it expires (tick Own Debuff). A missing debuff does not satisfy it, and a permanent one counts as never running out (it passes "is greater than" but never "is less than"), so pair it with NOT Debuff Present to also cover the debuff being absent. On Retail and WoW Forever the game hides many aura timers in combat, and the condition is then unavailable.
Example
your target has Sunder Armor where the remaining time is less than 3 seconds
Settings
What each setting in the condition editor means, from the game's own help.
Unit - The unit this condition uses as the target of comparison.
Own Debuff - Only consider auras that you applied yourself.
The icon next to the spell name will automatically update to display the spell that is currently selected. You can drag a new spell from your spell book or action bars into this icon slot to replace your selected spell.
Spell - This is a specific spell used in this condition. You may drag this spell from your spell book or action bars into the input field or spell icon to set this value. This input field has prediction enabled, so you do not have to type the full spell name, just select from the prediction frame when it appears.
Use this exact spell rank - Unticked, any rank of the spell matches: a numeric spell selection also recognizes auras with the same readable localized spell name. Ticked, only the exact spell ID you chose matches. Conditions saved before this option keep the exact ID until you untick it. Spell names already match by name. Unavailable metadata or restricted aura identity stays unavailable, including under NOT. Different spells sharing a name can match; tick the option when that distinction matters. (only on Classic Era, TBC Anniversary, Forever)
Operator - How to compare Debuff Time Remaining with the Seconds value. This comparison uses basic mathematical comparison operations.
Seconds - Remaining aura time is measured in seconds. Permanent auras have no expiration and do not satisfy a finite refresh threshold. An absent aura does not satisfy this condition. Restricted or unknown timing is unavailable, including under NOT.