And from the day on which you bring the sheaf of elevation offering—the day after the sabbath—you shall count off seven weeks. They must be complete:

(9) GOD spoke to Moses, saying: (10) Speak to the Israelite people and say to them: When you enter the land that I am giving to you and you reap its harvest, you shall bring the first sheaf of your harvest to the priest... (15) And from the day on which you bring the sheaf of elevation offering—the day after the sabbath—you shall count off seven weeks. They must be complete:

I might think that he must harvest and count and bring in the daytime. It is, therefore, written "seven complete Sabbaths shall they be." When are they "complete"? When he begins at night.

And so we worked on, while half were holding lances, from the break of day until the stars appeared.

The status of twilight is uncertain, as it is unknown whether it is day, or night, or both, and uncertainty in the case of a rabbinic ordinance is ruled leniently. Therefore, in both cases the eiruv is acquired.

(22) It is a positive commandment to count seven complete weeks from the day the omer is brought, as [Leviticus 23:15] states: "And from the day after the Sabbath, you shall count... seven weeks."...

(24) This mitzvah is incumbent on every Jewish male in every place and at all times.

This mishna determines the times beyond which the different prayers may not be recited. According to the Rabbis, the morning prayer may be recited until noon. Rabbi Yehuda says: It may be recited only until four hours after sunrise. According to the Rabbis, the afternoon prayer may be recited until the evening. Rabbi Yehuda says: It may be recited only until the midpoint of the afternoon [pelag haminḥa], i.e., the midpoint of the period that begins with the sacrifice of the daily afternoon offering and ends at nightfall, which is the end of the afternoon. The evening prayer may be recited throughout the night and is not fixed to a specific hour. According to the Rabbis, the additional prayer may be recited all day. Rabbi Yehuda says: It may be recited only until seven hours after sunrise.

Now that the halakha was stated neither in accordance with the opinion of this Sage [i.e. the Rabbis] nor in accordance with the opinion of that Sage [i.e. Rabbi Yehuda], one who acted in accordance with the opinion of this Sage has acted legitimately, and one who acted in accordance with the opinion of that Sage has acted legitimately, as this halakha is left to the decision of each individual.

The one who prays with the community during the day, he should count with them without a blessing. And if he remembers at night, she should bless and count.

If they (the people who are counting) made a mistake on a cloudy day and they blessed on the counting of the Omer, they should go back to count when it got dark. Those who are punctilious, they do not count until the stars come out [namely, three stars], and this is a proper thing to do.

Question: In many places, individuals and even Torah scholars conduct the bulk of their Purim meal ‎at night, going to shul and davening minchah but not maariv, then returning home and beginning ‎their meal by day and continuing into the night, such that most of the meal is at night. Is there logic ‎behind this custom, or not?‎

Answer: It appears to me that one should find some reason and support for this custom. I have ‎found a responsum which says, "I have heard from R' Toviah in the name of Riva that when youths ‎take food from each other, even without permission, for the joy of Purim, from the time the ‎megilah is read until the night of the Purim feast - two nights and one day - there is no issue of ‎surreptitious or overt theft. They should not be summoned to court and there is no concern, so ‎long as they do not overstep the practices established by the town councillors." It is clear that the ‎second night is legitimately part of the Purim feast. The question remains for Riva himself, fort he ‎second night is the 15th of Adar, and how could one fulfill the meal of the 14th on the 15th?... ‎Apparently, the reason is that the reading of the megilah on the morning of the 14th takes time, ‎and then one is busy sending portions and giving gifts to the indigent, and there is no time to eat a ‎meal with joy and pleasure. Therefore, our predecessors established part of the meal in the ‎evening, starting it during the day before maariv so as to fulfill the mitzvah of the feast during the ‎day, which is the essential time. One then continues during the time he has available, enjoying the ‎meal until night and at night, and the whole is one meal. We have found a similar practice of ‎nullifying a mitzvah meal for the sake of other mitzvot in Tosafot Chullin 83a, which asks why the ‎mishnah there did not include a meal for the first day of Succot among the four occasions when ‎people regularly eat large meals. He explained that it is because people are busy with the mitzvot ‎of Succah and Lulav on the day before Yom Tov, and so they did not prepare big meals for the first ‎day of Succot. Although I have justified this custom, still, my mentors customarily eat the essential ‎meal in the morning, as do I, and it appears that this is the practice in the Rhineland.‎