If a person forgot to count the Omer at night, and also forgot during the following day, but remembered shortly after sundown, may he still count the Omer? Let us take the example of a person who forgot to count the 26th night of the Omer, and forgot also the following day, until a few minutes after sunset. It is obvious that he cannot count with a Beracha, since one does not recite the Beracha if he forgot to count at night and counts the following day. The question, however, is whether he can count the 26th day without a Beracha and then count the 27th day that night, after dark, with a Beracha, just as one would if he counted during the day before sundown. The 13.5-minute period immediately after sunset, which is called "Ben Ha’shemashot," is a time of "Safek" (uncertainty), which means that it is uncertain whether it is regarded as daytime or nighttime. The question thus becomes whether counting the Omer during this period fulfills the previous day’s counting, or whether we must consider the possibility that the subsequent day has already begun, such that it is too late to count the previous day’s counting.
This issue is subject to a debate among the Halachic authorities. The Hid"a (Rav Haim Yosef David Azulai, 1724-1806), in his Birkeh Yosef, writes that in such a case one cannot continue counting with a Beracha. Hacham Ovadia Yosef, however, in his Hazon Ovadia – Hilchot Yom Tov (p. 238), disagrees, and claims that counting the Omer during "Ben Ha’shemashot" suffices to allow one to continue counting with a Beracha. He adds, however, that a person in this case must ensure throughout the remaining nights of the Omer to count after "Ben Ha’shemashot." Since he has established that he considers this period daytime, he can no longer do the nighttime counting during "Ben Ha’shemashot," as he would then be acting in a self-contradictory manner.
Rav Yaakob Haim Sofer (Baghdad-Israel, 1870-1939), in his Kaf Ha’haim (#83), writes that a person in this case should ensure henceforth to hear the Beracha recited from somebody else, rather than actually recite the Beracha, in order to satisfy all views. One who wishes to follow this stringency may certainly do so, but according to the strict Halacha, an individual in this case may continue counting with a Beracha, provided that he ensures to count after "Ben Ha’shemashot," as discussed.
Summary: If one forgot to count the Omer at night and also during the next day, but he counted during the 13.5-minute period after sundown, he may continue counting on subsequent nights with a Beracha. He must, however, ensure from that point on to count after this 13.5-minute period, since he has established that he treats this period as daytime. One who wishes to be stringent and satisfy all views should try to hear the Beracha from somebody else for the rest of the Omer period, rather than recite the Beracha himself.
