Q. I'm planing to make a siyum before Shavuos, is doing it on Yom Hameyuchas a desired day to celebrate with a Siyum?
A. Yom Hameyuchas is a day of distinction, it is the second day of Sivan and the forty-sixth day of the Omer. It is also the day before the beginning of the Shloshes Yemei Hagbalah, or the Three Days of marital restraint, that Moshe Rabbenu commanded the Jewish People to observe.
Yichus stands for being of distinguished lineage. There are a number of reasons for this day and the name it carries.
One common explanation is based on Talmud (Shabbos 86b-87a). The second of Sivan was the day when Hashem chose our Nation to become the "Mamleches Cohanim V'goy Kadosh — a priestly nation and a holy people".
When Moshe Rabbenu delivered this message the People answered, “Everything that Hashem has commanded we will do” (Shemos 19: 8)
The Aruch Hashulchan, (Orach Chaim 494: 7), explains that this is the reason why it is called Yom Hameyuchas — the day upon which we as a Jewish people attained our distinguished place among the family of nations.
Another reason quoted is that Judaism, is fundamentally a meritocracy. A person is rewarded for his own achievements, not those of his father’s or his sons.
Others suggest that in fact the day itself has no special or unique quality, but rather since it sits squarely between
Rosh Chodesh on the previous day and the Shloshes Yemei Hagbalah, it too is swept up in the overall simcha of the period. As such, Yom Hameyuchas achieves its prestige from its proximity to the holy days that surround it.
Horav Shlomo Miller's Shlit'a opinion is that one should do the Siyum as soom as possible.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a.