Firstborn men who attend a Siyum on Ereb Pesah to absolve themselves from Ta’anit Bechorim (the fast of the firstborn) should try to listen to the Siyum. It is not enough to be in attendance and then partake of the food; they should try to listen and understand the words of Torah spoken at the Siyum. The Rabbi making the Siyum should use the opportunity to share words of Torah and inspiration in order to encourage the people to allocate time for Torah learning.
The firstborns must ensure to eat a Ke’zayit of food at the Siyum. Some people make the mistake of taking a small piece of cake and drop of wine, and then leaving, thinking that they’re then covered and do not have to fast. In order to be exempt from the fast, one must participate in the Se’udat Misva, which requires eating a Ke’zayit.
One does not absolve himself from the fast by sending somebody to hear the Siyum and participate in the Se’uda in his place. One who did not personally attend the Siyum must fast, even if he sent somebody to the Siyum.
If a firstborn arrives at the Siyum late, after the Rabbi completed the Masechet, he may not join the Se’uda, and he is not absolved from the fast. However, Rav Pinhas Zebihi (contemporary) writes in his work on the laws of Pesah (p. 194) that if a person came while the Rabbi was speaking words of Musar after having completed the Masechet, he may be allowed to remain for the Se’uda, since he did, after all, participate in the learning.
There is a debate among the Halachic authorities as to whether completing Masechet Tamid – a very small Talmudic tractate – suffices for the Siyum of Ta’anit Bechorot. When the need arises, one may rely on the lenient view and make a Siyum on this Masechet.
If a woman studies a complete Masechet, she cannot absolve the firstborn from the obligation to fast through her Siyum.