Field Duration is a suffix that turns up on Off Hand, but only on gear tagged guardian_dome. It gives kitFieldTicksPercent: +10% to +12% at its lowest step, +38% to +40% at its best — and you need item level 116 before the best one can appear at all.
It comes up at weight 5 when the game rolls affixes, never doubles up with another affix that does the same job (kitFieldTicksPercent), and it is what puts Persistence, Permanence, the Long Watch, the Standing Guard and the Eternal Vigil in an item's name — so you might pick up a Wand of Persistence.
No Unique carries it at a fixed number.
Every step
10 steps · lowest to best
| Tier | Needs item level | Gives | Suffix word | Reads as |
|---|---|---|---|---|
| T1 | 1 | +10% to +12% | Persistence | Wand of Persistence |
| T2 | 6 | +13% to +15% | Persistence | Wand of Persistence |
| T3 | 14 | +16% to +18% | Permanence | Wand of Permanence |
| T4 | 24 | +19% to +21% | Permanence | Wand of Permanence |
| T5 | 36 | +22% to +24% | the Long Watch | Wand of the Long Watch |
| T6 | 55 | +25% to +27% | the Long Watch | Wand of the Long Watch |
| T7 | 75 | +28% to +30% | the Standing Guard | Wand of the Standing Guard |
| T8 | 92 | +31% to +33% | the Standing Guard | Wand of the Standing Guard |
| T9 | 105 | +34% to +37% | the Eternal Vigil | Wand of the Eternal Vigil |
| T10 | 116 | +38% to +40% | the Eternal Vigil | Wand of the Eternal Vigil |
Where you will see it
16 bases it can land on