Question No. 49:
When does the twenty-four-hour day begin–at sunset, at sunrise, or at midnight?
The twenty-four-hour cycle begins at sunset, because at the moment the earth came into existence and began to rotate on its axis, there was no light “upon the face of the deep,” whereupon “God said, Let there be light: and there was light….And the evening and the morning were the first day.” Gen. 1:2, 3, 5.
The “light” which shone on the first day, and by which God divided the day from the night (set the earth revolving on its axis), was not, however, that of the sun, for the sun and the moon were not created until the fourth day, when He spoke them forth “to rule over the day and over the night” (Gen. 1:18), which He had beforehand established.
Thus it was that whereas the earth began punctuating eternal time with the first night of creation week, from which the weekly seventh-day Sabbath is measured; the moon began punctuating time at the end of the third day and at the beginning of the fourth night from which the month is measured; and the sun began to punctuate time at the end of the fourth night and the beginning of the fourth day, from which the year is measured. Accordingly, the time-span which measures and segments the week, is three days in advance of the time-spans which measure and segment the solar year and the lunar month. In order, therefore, that His people might commemorate the week of creation, from the instant that the span of earthly time began, God commanded: “From even unto even, shall ye celebrate your sabbath.” Lev. 23 :32.
So the twenty-four-hour day begins with the night, at sunset; and the daytime itself, separate from the nighttime, begins at sunrise.