Until When to Count
9) The Omer must be counted before the break of dawn. If one forgot to count for the duration of the night, he must count during the next day, without a blessing. This allows him to continue to Count the Omer (with a blessing) for the remainder of the count.
10) In northern countries, the break of dawn can be as early as midnight.
Other Time-Related Laws
11) If one forgot to count for the entire night and the following day, but remembered during the time of bein ha-shemashos and counted the Omer, authorities dispute whether he may continue to Count the Omer for the remainder of the count. One may be lenient in this matter (and continue to count).
12) One who forgot to count the Omer on Friday, and remembered only after he accepted Shabbos (for instance, after a woman lights candles, by which she accepts Shabbos), may count the Omer (without a blessing) before night, and continue to count the Omer (from Shabbos and on) with a blessing.
13) The same applies to one who only remembered to count the Omer after praying Arvis (before night). He should count before nightfall, and may continue to count on the following night.
14) One who forgets to count for an entire night and day cannot continue to count the Omer with a blessing on following nights. Yet, he must continue to count without reciting a blessing. Some add that he should recite: “Yesterday was such and such, and today is such and such, of the Omer.”
15) One should preferably pray the Arvis prayer in advance of counting the Omer. With the exception of the first night, one who prays Arvis with a late minyan need not count the Omer at the beginning of the night, but should count after the Arvis prayer (together with the congregation).
16) The count of the Omer is recited before the Aleinu prayer; some count after the Aleinu prayer.
17) On Motzaei Shabbos, in places where the Veyiten Lecha prayer is recited, the Omer is counted before the prayer, after Kaddish.
18) One who arrives late in shul, such that the congregation counts the Omer before he has prayed, should count together with the congregation, and pray later.
19) Likewise, one who arrives in shul in time to commence the Amidah prayer with the congregation, whose must pray the Amidah prayer immediately and only then recite the Shema and its blessings, should pray the Amidah and then count the Omer with the congregation. Only after counting the Omer should he return to recite the Shema with its blessings.
20) One who prays at home (without a quorum) should count the Omer at the beginning of the night, after praying the Arvis prayer. However, one who is unable to pray the Arvis prayer at the beginning of the night may delay the counting of the Omer until later, on condition that he appoints somebody to remind him to count whenever he prays the Arvis prayer.
21) In chutz la-aretz, where two days of Yom Tov are observed, and the first day of the Omer count is the second day of Yom Tov, some count immediately after Arvis, and some count after the completion of Seder Night. A person should follow the custom of his place.
