וַיַּשְׁכֵּ֨ם אַבְרָהָ֜ם בַּבֹּ֗קֶר וַֽיַּחֲבֹשׁ֙ אֶת־חֲמֹר֔וֹ וַיִּקַּ֞ח אֶת־שְׁנֵ֤י נְעָרָיו֙ אִתּ֔וֹ וְאֵ֖ת יִצְחָ֣ק בְּנ֑וֹ וַיְבַקַּע֙ עֲצֵ֣י עֹלָ֔ה וַיָּ֣קָם וַיֵּ֔לֶךְ אֶל־הַמָּק֖וֹם אֲשֶׁר־אָֽמַר־ל֥וֹ הָאֱלֹהִֽים׃
И встал Авраам рано утром, оседлал задницу свою и взял с собою двух своих юношей и Исаака, сына его; и отколол дрова для всесожжения, и встал, и пошел к месту, о котором сказал ему Бог.
Mishneh Torah, Circumcision
Circumcisions are only performed during the daytime after sunrise, whether the operation takes place on the eighth day, the regular time, or subsequently, from the ninth day and further on, as it is said "on the eighth day" (Gen. 17:12) i.e. by day, and not at night. If the circumcision takes place after daybreak, it is correct. The whole of the day is proper for circumcision. Still it is a duty to perform it in the early part of the day, for the zealous fulfill their religious obligations at the earliest possible time.