On the night before Pesach, we are required to perform Bedikat Chametz – the search for Chametz in our home. The time for the search begins at nightfall. According to Ha’Rav Ovadyah Yosef (a”h), nightfall, “Tzet Ha’kochavim,” occurs in Eretz Yisrael approximately 20 minutes after sundown. In New York City, it occurs 35-40 minutes after sundown.
The halachah forbids performing certain activities from a half-hour prior to Bedikat Chametz, until one completes the search. Chachamim were concerned that a person who begins involving himself in other mundane activities may forget to perform the bedikah. It is likewise forbidden to eat bread or mezonot items in an amount exceeding a ke’beitzah (2 oz). It is therefore forbidden to eat a slice of pizza during Bedikat Chametz.
The Shulchan Aruch also includes Torah study in the list of activities forbidden during Bedikat Chametz. However, unlike the other activities, Torah learning is permissible within a half-hour prior to the Bedikah itself. This halachah, however, applies only to private study. A group session, such as a Shiur delivered in a shul, may be held during this period, as the members of the group will undoubtedly remind each other to search for Chametz after the learning session.