The new moon is sighted just after sunset, and it is the sign for the new month (Gen. 1:14). There is a tradition that new moons should be sanctified, supposedly derived from Exodus 12:2. But this verse does not say to sanctify the new moon. It only says that the new moon pointed out to Moses at the time would be the first day of that year. No details are given on how that was determined in that year or any other year in Exodus 12:2. These details have to come from putting together other scriptures. Besides the implication that there must be some way of figuring the first month for every year there is no command to sanctify the new moon in this text. There is a command to offer a special ascending offering on the day following the sighting of the moon and also to blow the trumpets over these offerings. The offerings themselves burn for a day and a night (Lev. 6:9-10). Ancient Israel innovated the custom of abstaining from commerce on the new moon day and also holding a feast, at which it was customary to practice ritual cleanliness. The custom is mentioned in 1 Sam. 20 and Amos 8:5. Neither passage is an absolute command, but rather they give us details of the tradition. Amos brings up the practice because those who wanted to practice deceit in the markets could not do so when the new moon was celebrated this way. He is disapproving of morally incorrect behavior, not giving absolute divine sanction to the custom. The Samuel passage merely reports the customary manner of celebrating the new moon. The custom is harmless enough, though, and serves the purpose of highlighting the start of a month, and the drawing of attention to the special treatment of the day at the Temple. When the kingdom is established again, it will help the whole community keep track of time properly, and it will also be marked by special worship services (cf. Isa. 66:23).
The days of a month are counted with the first day following the return of the lighted moon after a period of darkness from the previous month. The counting of days, according to the lighted portion of the day (dawn to dusk) does not vary. For this reason, careful chronology requires attaching the day numbers to the lighted portion of each day (dawn to dusk). If a Sabbath occurs on the 10th day of a month, then it will be reckoned as including the night previous. If, however, ascending offerings are made on the 10th day of a month, then those offerings are for a day and a night, and the day ends with the next dawn. In both cases, the same day is the 10th day, but according to the requirements of observance, either Sabbath or sacrifice, the night before or after the day is counted with it.
The ordinary reckoning of days of a month is from dawn to dawn. The night following is included with the day. This pattern harmonizes with natural waking and sleeping patterns. Sleeping is considered to be between days, and waking is for a day and part of a night. Tomorrow is considered to be after the sleeping time, even when it is already night. Michal told David during the night that if he did not escape, then he would be slain tomorrow (cf. 1 Sam. 19:11). When David battles with Amalek he battles from dawn twilight to dusk of their tomorrow (1 Sam. 30:17, Hebrew text). The Egyptian, on the other hand, counted three days and three nights as a day and a night each (cf. 1 Sam. 30:12). For Egyptians and Israel the day began at dawn.
The day was counted from dawn by John (cf. John 19:14). The sixth hour is calculated from dawn, and is about midday. Mark, also counting from dawn reckons the crucifixion at the third hour (cf. Mark 15:25). This also is counted from dawn. Modern people have difficulty with these two times, since they appear discrepant. However, upon reflection of the fact that a day was counted by dividing into thirds, the third hour, the sixth hour, and the ninth hour (cf. Mat. 20:3-5), the discrepancy disappears. These hours were ways of estimating thirds of a day in an era when the common man did not carry a clock. The third hour ranged between 7:30 and 10:30 and not just at the precise time of 9:00 am. The sixth hour ranged from 10:30 to 1:30. We see that these two times have 10:30 in common. So the time of the crucifixion was such that it was hard to judge precisely whether it had passed the period of the third hour into the beginning of the sixth when the crucifixion started. Now it ended about the 9th hour of the day, which also has to be 1:30 to 4:30. Custom also dictated the common use of the 1st hour of the day and the 11th hour when it was clear that the sun was just risen or close to setting. Any other more precise time given in accounts was probably because the author had noted the time on a sundial or had done calculations. All these hours were counted from dawn.
In Gen. 19:34, Lot’s daughter said to his younger daughter on the next day after she had lain with him that the younger daughter should do the same the coming night. In her reckoning the night she had lain with Lot was counted on the previous day, “I have lain yesterday with my father,” because the narrator introduces the verse with “tomorrow.” The word for yesterday in Hebrew is אֶמֶשׁ, regarded as a synonym of תְמוֹל. Translators like to render it “last night,” or “yesternight.” The word for “tomorrow” is a contraction yom aɦar, i.e. maɦarat, meaning “day after.” That this phrase denotes a time at the end of night, and not at the end of day, is proved in 1 Sam. 19:11 and Exodus 17:9. Amalek came to do battle with Israel, and it was known the battle would be joined at dawn. And it is reported that it ended at sunset. Moses said he would stand on the hill “tomorrow,” and evidently he did not mean all night before the battle.1
1. Some authors try to explain Gen. 19:34 by referring the word “tomorrow” to sunset, saying that the older daughter spoke to the younger after sunset. This is a cause of circular reasoning. It is assumed that maɦarat means sunset because it is assumed that a day begins at sunset. But definitive contexts prove that the epoch of this word is in the morning, and the contraction is clearly from “day after” (cf. Gen. 30:6).