Jamieson, Fausset & Brown, on Gen 1:5

“And he called the light Day, and the darkness Night; and there was evening and morning one day.”

“first day--a natural day, as the mention of its two parts clearly determines; and Moses reckons, according to Oriental usage, from sunset to sunset, saying not day and night as we do, but evening and morning.”

Imported from an open dataset — not yet checked against the printed edition.