The sale must take place while it is still permitted to derive benefit from ĥametz, for when the sixth hour of the day of the fourteenth of Nisan arrives, and it becomes forbidden to derive benefit from ĥametz, it likewise becomes forbidden to sell it. Instead, it must be destroyed. In order to allow people to sell their ĥametz until the very last minute, mekhirat ĥametz takes place on the fourteenth, just before the end of the time that it is permissible to derive benefit from ĥametz.
The prohibition takes effect according to one’s location. In Israel, the sixth hour arrives approximately seven hours before the East Coast of the United States. Therefore, a U.S. resident who is in Israel must sell his ĥametz in Israel, because if he sells his ĥametz according to the deadline in the United States, the sale will take place after the onset of the prohibition incumbent upon him. The end of Pesaĥ also poses a problem for such a person, because he must observe yom tov sheni shel galuyot (the extra day of Yom Tov observed in the Diaspora), which means that the prohibition of ĥametz applies to him until the end of the eighth day, while in Israel the ĥametz is bought back from the gentile after the seventh day. However, in fact, it is not a problem for him to sell his ĥametz in Israel. Even though the gentile sells the ĥametz back at the end of seven days, since the U.S. resident is still observing Pesaĥ according to the custom of Jews in ĥutz la-aretz, and he is not yet interested in buying the ĥametz back, the ĥametz remains hefker or in the possession of the beit din (rabbinical court). Only after yom tov sheni shel galuyot has passed does the ĥametz return to his possession.
If his family remains in the United States, and they plan to eat the ĥametz after the prohibition has commenced in Eretz Yisrael, he must renounce ownership of his portion in that ĥametz, and his family sells the ĥametz there (Sidur Pesaĥ Ke-hilkhato 11:14).
A resident of Israel who travels to the U.S. may, in principle, sell his ĥametz in the United States, for, according to most poskim, the obligation to eliminate ĥametz depends on the owner’s location, not the location of the ĥametz. Nevertheless, one should preferably sell it in Eretz Yisrael, in order to satisfy the opinions of all poskim, for some maintain that one must eliminate ĥametz according to its location, and, if this is the case, one must sell the ĥametz before the onset of the prohibition in Eretz Yisrael.
Additionally, a resident of Israel who is visiting a Diaspora community should not eat ĥametz on the eighth day of Pesaĥ, just as he should not do any other activity forbidden on yom tov, even in private (AHS 596:5). If such a person has his own place of residence, he need not partake in a second Seder. However, if he is being hosted by people who live abroad, he should participate in the second Seder. He should not recite berakhot on mitzvot, but instead should answer “Amen” to the berakhot of others.
. Oneg Yom Tov (§36) states that we follow the location of the ĥametz. Many disagree with this ruling and maintain that the prohibition takes effect according to the location of the owner. This is the opinion of Ĥessed Le-Avraham 141:35, Eretz Zvi 1:83, Mikra’ei Kodesh Pesaĥ 1:55, and other poskim quoted in Piskei Teshuva 443:1. Le-khatĥila, we take both opinions into consideration and follow whichever time is earlier, as is written in Igrot Moshe OĤ 4:94-95.
A Diaspora resident who is presently in Israel and sells his ĥametz in Israel should have in mind not to reacquire this ĥametz until after the festival ends in the Diaspora, as written above. Even if he did not have this intent, Sidur Pesaĥ Ke-hilkhato 11:35 states that presumably he does not want to reacquire the ĥametz before the festival ends, so he does not reacquire it until it becomes permissible. Mikra’ei Kodesh Pesaĥ 1:76 states that even if one acquired ĥametz on the eighth day of Pesaĥ in the Diaspora, the ĥametz may be eaten after Pesaĥ, since there are poskim who maintain that a Diaspora resident in Israel is not required to observe two days of yom tov. Therefore, since this is an uncertain situation on the rabbinic level, we are lenient.