Three men who ate a meal together (with bread) must recite a Zimun before Birkat Ha’mazon. Occasionally, three men eat together but their schedules do not coincide. Some people eat more quickly than others, and it sometimes happens that some of the meal’s participants wish to leave before the others. The Gemara establishes that if three men eat together and two wish to leave, the third must interrupt his meal to join them for a Zimun. As the two men are the majority, the third does not have the right to insist that they wait for him to finish his meal.
At one point may the third individual resume his meal?
This issue is subject to a debate between Rav Nahman and Rav Sheshat, two Sages in the Talmud. One view maintains that the third individual may resume eating immediately after the Zimun, meaning, once he recites, "Baruch She’achalnu… Hayinu." The second view, however, maintains that the person may not resume his meal until after the other two complete the first Beracha of Birkat Ha’mazon, meaning, until they recite "Baruch Ata Hashem Ha’zan Et Ha’kol."
The Shulhan Aruch codifies the lenient view, allowing the third person to resume eating immediately upon the completion of the Zimun, whereas the Rama (Rabbi Moshe Isserles, Poland, 1525-1572) rules that he must wait until the other two finish the first Beracha of Birkat Ha’mazon. Therefore, whereas Ashkenazim follow the stringent view, Sepharadim accept the Shulhan Aruch’s ruling, and allow the third individual to resume his meal immediately after participating in the Zimun. Interestingly, the Ben Ish Hai (Rabbi Yosef Haim of Baghdad, 1833-1909) accepts the Rama’s stringent ruling, instead of the lenient position of the Shulhan Aruch. Halacha (for the Sepharadim), however, follows the Shulhan Aruch’s position, and therefore the third person who interrupted his meal for a Zimun may resume eating immediately after the Zimun.
It should be noted that the individual does not even have to wait for the one leading the Zimun to repeat the response, "Baruch She’achalnu Mishelo…" As soon as he completes his response of "Baruch She’achalnu," he may resume eating at that point.
(See also the Halacha entitled "Reciting a Zimun When Some Participants of the Meal Want to Leave," dated 7/9/2009.)
Summary: If three people ate a meal together and two of them wish to leave before the third finished eating, the third must interrupt his meal to participate in a Zimun. According to Sephardic practice, he may resume eating immediately after answering the Zimun. According to Ashkenazic practice, he may not resume his meal until the other two have completed the first Beracha of Birkat Ha’mazon.
