It is forbidden to eat a large meal anytime on Ereb Shabbat, from the morning until the onset of Shabbat. We refer here to a large feast that one does not ordinarily eat during the week, except on special occasions. Of course, one may eat normal meals that he ordinarily eats during the week; this prohibition applies to the kind of meal that one does not normally eat.
There are a number of exceptions to this rule. Hacham Ovadia Yosef rules that it is permissible to conduct a large meal to celebrate a Berit Mila or Pidyon Ha’ben. This applies even in the case of a Berit Mila held after the infant’s eighth day, or a Pidyon Ha’ben held after the thirtieth day. Even though these occasions take place later than the optimal time, they warrant a large celebration that overrides the prohibition against eating large meals on Ereb Shabbat. Hacham Ovadia adds, however, that in such situations, the meal should be held specifically during the morning hours, before midday, to show honor to Shabbat.
A Bar Misva celebration, too, may be held on Friday morning. The Zohar Hadash emphasizes the importance of holding a celebration to mark the occasion of a Bar Misva, comparing the Bar Misva meal to the meal conducted at a wedding. If the child’s thirteenth birthday falls on Ereb Shabbat, and the parents wish to make a celebration on that day, they may conduct a large, lavish feast on Friday morning. It must be emphasized that the meal should preferably be held in the morning, before midday.
Hacham Ovadia writes that if a person completes a Masechet (Talmudic tractate) on Friday, and he wants to host a large Siyum celebration, then he should delay the celebration until after Shabbat. Although it is certainly worthwhile and important to make a Siyum celebration upon completing a Masechet, one who plans on making a large meal in honor of this occasion should not schedule such an event for Friday – even Friday morning – and should instead delay the celebration until Mosa’eh Shabbat or Sunday.
Summary: It is forbidden to eat anytime on Friday a meal that is larger than the meals he ordinarily eats during the week. The exceptions to the rule are large meals that celebrate the occasion of a Berit Mila, Pidyon Ha’ben or Bar Misva, which may be held on Friday morning, but preferably not on Friday afternoon. A large meal to celebrate the completion of a Masechet should not be made on Friday.