Why does the Torah insert the words "be'Yom Tzavoso"?
Rashi (in Bo, 12:2): To teach us that Hashem only spoke to Moshe in the daytime.
Zevachim, 98a: To teach us that Korbanos may only be brought in the day and not in the night.
What is "Asher Tzivah Hashem es Moshe be'Har Sinai" referring to?
Ramban #1 and Moshav Zekenim #1 (both citing the Sifra): It refers to all the Mitzvos, which were said on Har Sinai (with all their details), some of which were repeated in the Ohel Mo'ed.
Ramban #2: It refers to the Milu'im, the Olah and the Chatas, which were said on Har Sinai; whereas the end of the Pasuk "Lehakriv es Korb'neihem la'Hashem be'Midbar Sinai" refers ro the Minchah the Asham and the Shelamim, in the Ohel Mo'ed.
Ramban #3 and Moshav Zekenim#2: "be'Har Sinai means (not on Har Sinai, but) in front of Har Sinai 1 - in the Ohel Mo'ed. 2
As in Pinchas, Bamidbar, 28:6 "Olas Tamid ha'Asuyah beHar Sinai (Ramban), See also Beha'aloscha, Bamidbar, 10:33 and Devarim, 1:6, where "me'Har Hashem" and "ba'Har ha'Zeh", respectively, mean 'from in front of the Mountain' and 'in front of this Mountain' (Ramban).
Ramban: And the reason that the Pasuk mentions both Har Sinai and Midbar Sinai is to stress that the Korbanos were commanded not on the Mountain, where the Shechinah rested, and not in the desert after they left Har Sinai, but in the desert, in front of the mountain, where the Mishkan was standing.
The Gemara in Zevachim 98a learns from "be'Yom Tzavoso" that Korbanos are offered only during the day. If so, why does Kidushin 36a need Pesukim to exclude women from Semichah, Tenufah and Hagashah, seeing as they are exempt from Mitzvos Asei she'ha'Zman Gerama?
Moshav Zekenim: Even though women are exempt, without a special D'rashah we would not know that if they did perform them the Korban is Pasul.
Why do we need "be'Yom Tzavoso" to teach that Korbanos are offered only during the day, bearing in mind that we learn from "Shiv'as Yamim Tih'yeh im Imo" that one may be Makdish an animal on the eighth night, and offer it the next day?
Perhaps "Shiv'as Yamim?" teaches only le'Chatchilah, and only about animals, whereas "be'Yom Tzavoso" comes to incorporate teaches about all Korbanos, and even Bedi'eved (PF). 1
Becaise in the realm of Kodshim, something is Me'akev only if it is mentioned twice (Tosfos Pesachim 11a DH Kotzrin).