"Grieve at night, thy tears of sorrow.
Grieve in light, the days that follow,
Descend like snow."
1. A second, established reference to grief/sorrow bringing darkness - "Breed my night with thy sorrow." Thus, grief, night, darkness.
2. Constant, non-stop grief - both night and day (light)
3. Light + daytime
4. Days following, one after another, never-ending, drifting, slowly falling, like snow, frozen in grief.
5. The lyrics are probably meant to make sense.