Day: Natural, from Evening to Evening
Source: TTT
Genesis 1:5
God called the light “day,” and the darkness He called “night.” And there was evening, and there was morning—the first day.
Leviticus 23:32
It will be a Sabbath of complete rest for you, and you shall humble yourselves. From the evening of the ninth day of the month until the following evening you are to keep your Sabbath.”