The Rain of Rust Feat says: "You conjure a red raincloud in a 10-foot burst within 60 feet, which pours rust-colored rain directly below it. Any creature in the rain with the metal trait, that is made of metal, or is wearing metal armor is covered in corrosive build-up. Any such creature is clumsy 1 as long as it remains in the area. If such a creature is in the rain at the start of its turn, it takes 3d6 damage with a basic Fortitude save against your class DC, plus 1d6 persistent damage if it fails. Damage from this impulse ignores Hardness."
What is the duration of this?
I expected SFS to issue a clarification on this and an area on the earth/water composite, but they didn't.