All chords on the harp are broken, either quickly, brisee, or arpeggiated, unless marked otherwise. In modern music you can choose to play them flat, but it will sound awkward and ugly (in some opinions). Chords are broken because it makes them easier to hear, is expressive, is musical tradition, they last longer, and it is unique now to the harp. Pianists used to break chords much more, and stopped doing it in the 1920s or so. Because it is tradition, you certainly do so in traditional music. Call it “period style” if you have to. Only the eighth-note fast-moving chords might be flat. And when you break them, the top note lands on the beat, not after.