On Which Days Is It Forbidden to Perform a Bris Milah Late?

Shalom,

A. One must not perform a bris milah late on Shabbat (Shulchan Aruch Orach Chaim 265:4, and Shulchan Aruch Yoreh De'ah 266:2).

B. One may not perform a bris milah late on Yom Tov (Shulchan Aruch Yoreh De'ah ibid.). This includes the second day of Yom Tov observed by diaspora communities (Shulchan Aruch Yoreh De'ah ibid. section 8), where it is explained that even a doubtful case of a delayed bris milah does not override the second day of Yom Tov. See the detailed discussion in Shut Yabia Omer, Part 8, Yoreh De'ah 23, and in the work Chazon Ovadia, Yom Tov, pp. 145-149.

C. According to Sephardic custom, one does not perform a bris milah that is certainly late on Thursday or Friday unless there is a clear local custom to perform it then; in that case, one follows the local custom. However, if the bris milah is only possibly late—i.e., the child was born Wednesday at twilight—it is permitted and required to perform the bris on the following Thursday, and it may not be postponed. Even if the child was born Monday at twilight and the next week Rosh Hashanah falls on Tuesday and Wednesday, it is permitted to perform the bris on Thursday. It is likewise permitted to perform a delayed bris milah before Yom Tov within three days. This enactment was made solely to prevent desecration of Shabbat, and the restrictions on Yom Tov are less stringent than Shabbat. Yom Kippur is treated like Shabbat in this regard (see in detail Shut Yabia Omer, Part 5, Yoreh De'ah 23).

D. The Ashkenazi custom is to perform a late bris milah even on Thursday and Friday (see Mishnah Berurah 265:33 citing the S'k from Yoreh De'ah 266, the Magen Avraham, and Eliyah Rabbah). It is noted in the work Nishmat Avraham, Yoreh De'ah 267:103, citing the Gaon Rabbi Shlomo Zalman Auerbach zt"l, that this is the common practice. Similarly, Rabbi Yitzchak Elishiv zt"l holds this view, as quoted in the book Ashrei HaIsh, Yoreh De'ah Part 2, Chapter 55, section 12. This is also supported in the responsa T'shuvot Vehanhagot, Part 2, siman 859.

 E. It is permitted to perform a late bris milah on Sunday (see Shut Divrei Yatziv Part 2, Yoreh De'ah 110, and Shut Cheshev HaEfod Part 3, siman 47). 

With blessings,

 Hillel Meirs