The earliest time for performing a Berit Mila in the morning is the point of Nes Ha’hama (sunrise). However, if the circumcision was performed earlier, it is nevertheless valid, as long as it was performed after the point of Amud Ha’shahar (when the first rays of light become visible in the eastern sky).
The Shulhan Aruch, in discussing the laws of Berit Mila, writes that a Berit should be performed early in the day, in fulfillment of the famous rule of "Zerizin Makdimin Le’misvot," which requires performing Misvot as soon as possible without unnecessary delay. This principle is learned from the example of Abraham Abinu, who arose early in the morning in order to comply with the command of Akedat Yishak ("Va’yashkem Abraham Ba’boker" – Bereishit 22:3).
In light of this Halacha, the Aruch Ha’shulhan (Rav Yechiel Michel Epstein of Nevarduk, 1829-1908) raises the question of why we do not perform a Berit Mila early in the morning, even before the Shaharit prayer. Why do we delay the Berit until after Shaharit, if the rule of "Zerizin Makdimin" requires performing the Misva as early as possible?
Numerous answers have been given to this question. One answer is that Shaharit should be recited before performing a Berit because of the rule of "Tadir Ve’she’eno Tadir, Tadir Kodem" – we perform a more frequent Misva before a less frequent Misva. Since the Misva to pray Shaharit is observed far more frequently than the Misva of Berit Mila, we first recite Shaharit before performing a Berit. (This is particularly so in light of the fact that Shaharit includes several Misvot – the Amida, Shema, Tallit and Tefillin.)
The Dibreh Malkiel (Rav Malkiel Tzvi Tannenbaum of Lomza, 1847-1910) writes (1:14) that we first recite Shaharit because its time frame is far more limited than that of Berit Mila. Shaharit must be recited by a certain time in the morning, whereas a person can be circumcised at any time during his lifetime. And although the Misva is to perform the Berit on the eighth day, it can be done at any point on the eighth day, until sundown, as opposed to Shaharit, which must be recited by the end of the fourth hour of the day. Therefore, we first perform the Misva with a shorter time frame, before performing the Berit.
Yet another reason that has been suggested is that the Torah speaks of performing Berit Mila on "Yom Ha’shemini" – the eighth day, whereas in reference to the Shaharit prayer, the Torah uses the word "Boker" (morning). We therefore first recite Shaharit, which is specifically associated with the morning, before performing a Berit, which is associated with daytime generally.
The work "Koret Ha’berit" (Rav Eliyahu Posek, 1859-1932) explains, very simply, that it is customary to drink the wine over which the Beracha is recited at a Berit, and it is forbidden to drink wine before reciting Shaharit. Necessarily, then, the Berit must be delayed until after Shaharit.
The Hazon Ish (Rav Avraham Yeshaya Karelitz, 1878-1953) ruled that one does not have to recite Shaharit immediately at sunrise on the day of a Berit in order to perform the Berit at the earliest possible time. It suffices to pray Shaharit at the time one normally prays and then perform the Berit afterward.
More generally, the Halachic authorities indicate that while a Berit should ideally be performed early, the requirement of "Zerizin Makdimin" is fulfilled as long as it is performed before Hasot (midday as defined by Halacha, namely, the midway point between sunrise and sunset). Thus, for example, the Shebut Yaakob (Rav Yaakov Reischer, 1661-1733), cited in Pit’heh Teshuba, criticizes the Hazanim who prolong the prayer service on Shabbat and Yom Tob when a Berit is performed, causing the Berit to take place after Hasot. It seems that Hasot marks the critical cutoff point with regard to the rule of "Zerizin Makdimin Le’misvot."
Should a Berit be postponed until the afternoon if this will allow more guests to participate? Does the value of "Be’rob Am Hadrat Melech" – performing the Misva in the presence of a large assemblage of Jews – supersede the value of "Zerizin Makdimin Le’misvot"?
Hacham Ovadia Yosef addresses this question in his work Yabia Omer (vol. 2, Yoreh De’a, 18), and he concludes that as long as a Minyan would be present without delaying the Berit, it should not be delayed. The Berit should be delayed until the afternoon only if this is necessary to assure the presence of a Minyan; if a Minyan can be assembled earlier, the Berit should not be delayed to allow for a larger crowd.
Interestingly, the Ma’aseh Roke’ah (cited in Machshireh Mila, 2:3) notes that there were occasions when a Berit Mila was delayed because of the women who needed time to put on their makeup and jewelry (listen to audio recording for precise citation). The Ma’aseh Roke’ah sharply denounces this practice, noting that although the Rabbis were unable to stop it, people should ensure to perform the Berit promptly.
One important exception to this Halacha must be emphasized. The work Kibbud Horim (chapter 12, note 17; listen to audio recording for precise citation) brings the ruling of Rav Yosef Shalom Elyashiv (1910-2012) that if the infant’s grandparents ask the parents to delay the Berit so they can attend, the parents should comply. Since the Berit can be performed the entire day, Rav Elyashiv explained, it is proper for the child’s parents to honor their parents’ wishes and delay the Berit, as this overrides the principle of "Zerizin Makdimin Le’misvot." Rav Elyashiv said that it is preferable to try to convince the grandparents to allow the Berit to be performed earlier, but if this is not possible, then the Berit should be delayed. Similarly, the author of the work "Ve’alehu Lo Yibol" relates that he posed the question to Rav Shlomo Zalman Auerbach (1910-1995) of whether a Berit may be delayed until the afternoon to allow family members to attend, and the Rabbi responded, "Titnaheg Ke’ben Adam" – "Act like a human being." For the sake of family members’ attendance, it is proper to delay a Berit, in consideration of their feelings, notwithstanding the general rule requiring performing a Berit Mila early in the day when possible.
Summary: It is proper to perform a Berit Mila as soon as possible after Shaharit, though one does not have to pray Shaharit at sunrise in order to perform the Berit at the earliest possible moment. Most importantly, the Berit should be performed before halachic midday. As long as a Minyan can be present earlier, a Berit should not be delayed until the afternoon to allow for a larger attendance. It should be delayed until the afternoon, however, to allow for the grandparents or other family members to attend.