The Torah requires a father to perform a Pidyon Haben one month after the birth of a firstborn son. (We will not discuss here the various conditions that must be met for this obligation to apply.) Specifically, the Pidyon Haben is performed on the child’s thirty-first day, including the day of birth. For example, if a boy was born on Wednesday, then the thirty-first day would be Friday, four weeks later. Since the Halachic day begins the previous night, the Pidyon Haben would be held on Thursday night. The Pidyon Haben cannot be performed on the thirtieth day, Thursday, because thirty full days must pass before the Misva may be performed.

Some authorities maintain that the Pidyon Haben may not be held until after a period of just over 29.5 twenty-four-hour cycles has passed since the child’s birth. This is the time-period of the monthly lunar cycle, and, according to some authorities, this period must pass before the Misva of Pidyon Haben may be performed. This position affects situations of a child born late in the afternoon, shortly before sundown. In the case mentioned above, for example, if the child was born before sundown on Wednesday afternoon, the thirty-first day begins on Thursday night four weeks later, as mentioned, but the period of 29.5 twenty-four-hour cycles does not end until sometime Friday morning. Thus, according to this view, the Pidyon Haben cannot be held on Thursday night in such a case. This is the position taken by Hacham Ben Sion Abba Shaul (Israel, 1923-1998), in his work Or Le’sion, Helek 2, page 153.

Hacham Ovadia Yosef, however, in Yabia Omer, Helek 9, page 251, disagrees, noting that numerous authorities, including the Magen Abraham, Aruch Ha’shulhan and Sedeh Hemed, dispute this view. Moreover, the Shulhan Aruch makes no mention of this requirement to wait the duration of a lunar cycle; he states simply that a Pidyon Haben is performed on the thirty-first day. It is inconceivable, Hacham Ovadia notes, that the Shulhan Aruch would have omitted such an important provision unless he decidedly ruled against it. We may therefore assume that this opinion was not accepted by normative Halacha, and the time for Pidyon Haben begins on the thirty-first day, regardless of whether or not the duration of a lunar cycle has passed since the child’s birth.

It must be emphasized that the converse is also true; meaning, a Pidyon Haben cannot be held on the thirtieth day, even if 29.5 twenty-four-hour periods have passed since the child’s birth. Since, as we saw, Halacha accepts the thirty-first day as the sole determining factor, under no circumstances can the Pidyon Haben be performed before the onset of the thirty-first day.

Summary: A Pidyon Haben is held on the thirty-first day since the boy’s birth, including the day of birth. Thus, for example, if the child was born on a Wednesday, in which case the thirty-first day is Friday four weeks later, then the Pidyon Haben should be held on Thursday night, as in Halacha the day begins on the previous night.