Where does “Dies” come from?

Dies comes from Latin dies, derived from Proto-Indo-European dyew-, meaning "to shine" or "daylight," which developed into the sense of "day."

Dies (English): One of the Protogenoi, the Protogenos personification of day. She is the daughter of fellow Protogenoi, Nox/Nyx (Night) and Erebus (Darkness), and sister-wife of Aether. She is the Roman counterpart of Hemera