Sunset usually means rest, but here it means the opposite. As the sun goes down and the sky "goes to sleep," the speaker imagines the world waking up, as if night is the moment people finally see clearly. What they wake from is "daylight lies" and "daily blindness," so the bright, busy day becomes a kind of false comfort, a time when people don't really look at what's going on.
The last four lines turn darker. "Screens and screams" run together, suggesting that media and noise blur into one another, and out of that noise come "the voices of power." Those voices also carry "the will of long dead heroes," which seems to hint that the past is being used to justify the present, though the poem leaves it open how the speaker feels about that. The mood is uneasy and suspicious, with a quiet sense of warning. There's no sunset beauty here, only a sense that the dimming light is when the truth shows up, and it isn't pleasant.