Jehovah God introduced this fundamental division of time on the first “day” of the period during which he prepared the earth for mankind, when diffused light evidently penetrated the swaddling bands, thus causing the moisture-covered earth to experience its first day and night as it rotated on its axis through the light of the sun. “God brought about a division between the light and the darkness. And God began calling the light Day, but the darkness he called Night.” (Ge 1:4, 5) Here the word “Day” refers to the daylight hours in contrast with the nighttime. However, the record thereafter goes on to use the word “day” to refer to other units of time of varying length. In both the Hebrew and the Greek Scriptures, the word “day” (Heb., yohm; Gr., he·meʹra) is used in a literal and in a figurative or even symbolic sense.

A solar day, the fundamental unit of time, is established by one complete rotation of the earth on its axis, as from the time the sun leaves a meridian, the highest point it attains at midday, until it returns to it. This solar or civil day is currently divided into two periods of 12 hours each. The forenoon period is indicated by the Latin ante meridiem (a.m.) and the afternoon period by the Latin post meridiem (p.m.). However, in Bible times various other methods were used for dividing the day.

The Hebrews began their day in the evening, after sunset, and ended it the next day at sunset. The day, therefore, ran from evening to evening. “From evening to evening you should observe your sabbath.” (Le 23:32) This follows the pattern of Jehovah’s creative days, as indicated at Genesis 1:5: “There came to be evening and there came to be morning, a first day.”​—Compare Da 8:14.

The Hebrews were not the only ones who reckoned a day from evening to evening; the Phoenicians, Numidians, and Athenians also did so. The Babylonians, on the other hand, counted the day from sunrise to sunrise; while the Egyptians and the Romans reckoned it from midnight to midnight (as is commonly done today).

Although the Hebrews officially began their day in the evening, they sometimes spoke of it as if beginning in the morning. For example, Leviticus 7:15 says: “The flesh of the thanksgiving sacrifice of his communion sacrifices is to be eaten on the day of his offering. He must not save up any of it until morning.” This usage was doubtless simply a matter of convenience of expression, to indicate overnight.

As mentioned in the creation account, the daylight period is also called day. (Ge 1:5; 8:22) In the Bible it is divided up into natural periods: the morning twilight or morning darkness, just before the day’s beginning (Ps 119:147; 1Sa 30:17); the rising of the sun or dawning (Job 3:9); the morning (Ge 24:54); noon or midday (De 28:29; 1Ki 18:27; Isa 16:3; Ac 22:6); the time of the sunset, marking the day’s close (Ge 15:12; Jos 8:29); and the evening twilight or evening darkness (2Ki 7:5, 7). The times for making certain offerings or the burning of incense by the priests were also time periods known to the people.​—1Ki 18:29, 36; Lu 1:10.

What is the time “between the two evenings”?

With reference to the slaying of the Passover lamb on Nisan 14, the Scriptures speak of “the two evenings.” (Ex 12:6) While some commentaries on Jewish tradition present this as the time from noon (when the sun begins to decline) on until sundown, it appears that the correct meaning is that the first evening corresponds with the setting of the sun, and the second evening with the time when the sun’s reflected light or afterglow ends and darkness falls. (De 16:6; Ps 104:19, 20) This understanding was also that offered by the Spanish rabbi Aben-Ezra (1092-1167), as well as by the Samaritans and the Karaite Jews. It is the  view presented by such scholars as Michaelis, Rosenmueller, Gesenius, Maurer, Kalisch, Knobel, and Keil.

There is no indication that the Hebrews used hours in dividing up the day prior to the Babylonian exile. The word “hour” found at Daniel 3:6, 15; 4:19, 33; 5:5 in the King James Version is translated from the Aramaic word sha·ʽahʹ, which, literally, means “a look” and is more correctly translated a “moment.” The use of hours by the Jews, however, did come into regular practice following the exile. As to “the shadow of the steps” referred to at Isaiah 38:8 and 2 Kings 20:8-11, this may possibly refer to a sundial method of keeping time, whereby shadows were projected by the sun on a series of steps.​—See SUN (Shadow That Went Ten Steps Back).

The early Babylonians used the sexagesimal system based on a mathematical scale of 60. From this system we get our time division whereby the day is partitioned into 24 hours (as well as into two periods of 12 hours each), and each hour into 60 minutes of 60 seconds each.

In the days of Jesus’ earthly ministry, the practice of dividing the daylight period into hours was common. Thus, at John 11:9 Jesus said: “There are twelve hours of daylight, are there not?” These were generally counted from sunrise to sunset, or from about 6:00 a.m. to 6:00 p.m. So, “the third hour” would be about 9:00 a.m., and it was at this time that the holy spirit was poured out at Pentecost. (Mt 20:3; Ac 2:15) When Jesus, tired out from a journey, was sitting at Jacob’s fountain it was about “the sixth hour,” or noon, which was also the time when Peter became very hungry at Joppa. (Joh 4:6; Ac 10:9, 10) It was also about noon when darkness fell over all the earth until “the ninth hour,” or about 3:00 p.m., when Jesus expired on the torture stake. (Mt 27:45, 46; Lu 23:44, 46) This ninth hour was also called “the hour of prayer.” (Ac 3:1; 10:3, 4, 30) So, “the seventh hour” would be about 1:00 p.m. and “the eleventh hour,” about 5:00 p.m. (Joh 4:52; Mt 20:6-12) The night was also divided into hours at that time.​—Ac 23:23; see NIGHT.

There are times when the Hebrews used ‘day and night’ to mean only a portion of a solar day of 24 hours. For example, 1 Kings 12:5, 12 tells of Rehoboam’s asking Jeroboam and the Israelites to “go away for three days” and then return to him. That he did not mean three full 24-hour days but, rather, a portion of each of three days is seen by the fact that the people came back to him “on the third day.” At Matthew 12:40 the same meaning is given to the “three days and three nights” of Jesus’ stay in Sheol. As the record shows, he was raised to life on “the third day.” The Jewish priests clearly understood this to be the meaning of Jesus’ words, since, in their effort to block his resurrection, they quoted Jesus as saying: “After three days I am to be raised up,” and then they requested Pilate to issue a command for “the grave to be made secure until the third day.”​—Mt 27:62-66; 28:1-6; note other examples in Ge 42:17, 18; Es 4:16; 5:1.

No names were used by the Hebrews for the days of the week, except for the seventh day, called the Sabbath. (See SABBATH DAY.) Reference was made to the various days by their numerical order. In the days of Jesus and his apostles, the day preceding the Sabbath was called the Preparation. (Mt 28:1; Ac 20:7; Mr 15:42; Joh 19:31; see WEEK.) The practice of naming the days after the names of the planets and other heavenly bodies was pagan. The Romans named the days after the Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn, but in northern Europe, four of these names were later changed into the Germanic equivalents of the Roman gods whom the days represented.

Sometimes the word “day” is used to indicate a measure of distance, as in the expressions “a day’s journey” and “a sabbath day’s journey.”​—Nu 11:31; Ac 1:12; see WEIGHTS AND MEASURES.

In prophecy a day is at times used to stand for one year. This can be noted at Ezekiel 4:6: “You must lie upon your right side in the second case, and you must carry the error of the house of Judah forty days. A day for a year, a day for a year, is what I have given you.”​—See also Nu 14:34.

Certain specific numbers of days given in connection with prophecies are: three and a half days (Re 11:9); 10 days (Re 2:10); 40 days (Eze 4:6); 390 days (Eze 4:5); 1,260 days (Re 11:3; 12:6); 1,290 days (Da 12:11); 1,335 days (Da 12:12); and 2,300 days (Da 8:14).

The term “day(s)” is also used with reference to a time period contemporaneous with a particular person, as for example, “the days of Noah” and “the days of Lot.”​—Lu 17:26-30; Isa 1:1.

Other cases where the word “day” is used in a flexible or figurative sense are: “the day of God’s creating Adam” (Ge 5:1), “the day of Jehovah” (Zep 1:7), the “day of fury” (Zep 1:15), “the day of salvation” (2Co 6:2), “the day of judgment” (2Pe 3:7), “the great day of God the Almighty” (Re 16:14), and others.

 This flexible use of the word “day” to express units of time of varying length is clearly evident in the Genesis account of creation. Therein is set forth a week of six creative days followed by a seventh day of rest. The week assigned for observance by the Jews under the Law covenant given them by God was a miniature copy of that creative week. (Ex 20:8-11) In the Scriptural record the account of each of the six creative days concludes with the statement: “And there came to be evening and there came to be morning” a first, second, third, fourth, fifth, and sixth day. (Ge 1:5, 8, 13, 19, 23, 31) The seventh day, however, does not have this ending, indicating that this period, during which God has been resting from his creative works toward the earth, continued on. At Hebrews 4:1-10 the apostle Paul indicated that God’s rest day was still continuing in his generation, and that was more than 4,000 years after that seventh-day rest period began. This makes it evident that each creative day, or work period, was at least thousands of years in length. As A Religious Encyclopædia (Vol. I, p. 613) observes: “The days of creation were creative days, stages in the process, but not days of twenty-four hours each.”​—Edited by P. Schaff, 1894.

The entire period of the six time units or creative “days” dedicated to the preparation of planet Earth is summed up in one all-embracing “day” at Genesis 2:4: “This is a history of the heavens and the earth in the time of their being created, in the day that Jehovah God made earth and heaven.”

Man’s situation does not compare with that of the Creator, who does not reside within our solar system and who is not affected by its various cycles and orbits. Of God, who is from time indefinite to time indefinite, the psalmist says: “For a thousand years are in your eyes but as yesterday when it is past, and as a watch during the night.” (Ps 90:2, 4) Correspondingly, the apostle Peter writes that “one day is with Jehovah as a thousand years and a thousand years as one day.” (2Pe 3:8) For man, a 1,000-year period represents some 365,242 individual time units of day and night, but to the Creator it can be just one unbroken time period in which he begins the carrying out of some purposeful activity and brings it on to its successful conclusion, much as a man begins a task in the morning and concludes it by the day’s end.

Jehovah is the Originator of our universe in which time, space, motion, mass, and energy have all been proved to be inescapably interrelated. He controls them all according to his purpose, and in dealing with his creatures on earth he makes definite time appointments for his own actions toward them, right down to the “day and hour.” (Mt 24:36; Ga 4:4) He keeps such appointments with the utmost punctuality.