Gemara

34a - Question: What is the source to exempt women from an Aseh sheha'Zman Gerama?

Answer: We learn from Tefilin. Just like women are exempt from Tefilin, they are exempt from every Aseh sheha'Zman Gerama.

Suggestion: We should learn from Hakhel that women are obligated!

Answer: Matzah and Hakhel are Shnei Kesuvim (two verses obligating women in an Aseh sheha'Zman Gerama), so they do not teach about other things.

35a - Question: One opinion learns from Shnei Kesuvim. What is his source?

Answer (Rava): "(You will wear Tefilin)... in order that Hash-m's Torah will be in your mouth" equates the entire Torah to Tefilin. Tefilin is an Aseh sheha'Zman Gerama, and women are exempt. They are exempt from every such Aseh.

Question: Some say that Tefilin is not Zman Gerama. How can they answer?

Answer: Matzah, Simchah and Hakhel are Sheloshah Kesuvim that obligate women. (All agree that we do not learn from Sheloshah Kesuvim.)

Pesachim 43b: "Lo Sochal Alav Chametz Shiv'as Yomim Tochal Alav Matzos" - whoever is commanded to eat Matzah, may not eat Chametz. Eating Matzah is Zeman Gerama. One might have thought that women are exempt from it, and also from the Lav of Chametz. A verse explicitly forbids Chametz to them, and therefore, they are commanded to eat Matzah;

(R. Elazar): "Lo Sochal Alav Chametz Shiv'as Yomim Tochal Alav Matzos" - whoever is forbidden to eat Chametz is commanded to eat Matzah.

Sukah 28a (Beraisa): "Ha'Ezrach" obligates women in Inuy (fasting on Yom Kipur).

Question: Another verse already equates woman to men for all punishments!

28b - Answer: "Ha'Ezrach" obligates women in the Mitzvah of Tosefes Inuy (to start fasting before night) for which there is no Lav or punishment.

Rishonim

Rif and Rosh (Kidushin 14b and 1:60): Women are exempt from a Mitzvas Aseh sheha'Zman Grama, such as Sukah, Lulav, Shofar, Tzitzis and Tefilin.

Rambam (Hilchos Avodah Zarah 12:3): Women are exempt from all Mitzvos Aseh that come from time to time and are not constant, except for Kidush ha'Yom, eating Matzah on the (Seder) nights of Pesach, eating and Shechitah of Korban Pesach, Hakhel and Simchah.

Lechem Mishneh: Some texts say 'Kidush Shabbos and Yom Tov'. Our text is better, for Kidush of Yom Tov is only mid'Rabanan. Kidush Yom Tov cannot refer to Melachah, for this is a Lav and women are obligated. Even though there is also an Aseh, he would not need to say that the Aseh applies to them, for in any case the Lav obligates them.

Yehudah Ya'aleh (1:82 DH v'Da): Kidush ha'Yom applies to women due to the Hekesh of Zachor to Shamor. Similarly, the Aseh of Yom Tov should apply to them, from a Hekesh "Shabboson Mikra Kodesh Kol Meleches Avodah Lo Sa'asu"! Why do Tosfos and the Rambam exempt women from the Aseh of Yom Tov? The text of the Rambam that obligates women in (the Aseh of) Yom Tov is proper. This is why burning Kodshim, Bris MIlah (after day eight) and Kisuy ha'Dam do not override the Lav of Yom Tov (even for women)!

Yehudah Ya'aleh (1:107 DH uv'Lav): The Gemara concluded that Matzah, Simchah and Hakhel are Sheloshah Kesuvim that obligate women, so we do not learn from them. Abaye exempts them from Simchah! Why didn't we bring another Mitzvah for which all agree that they are obligated, such as destroying Chametz (on Erev Pesach), Shabboson of Shabbos and Yom Tov, Inuy of Yom Kipur and telling about Yetzi'as Mitzrayim on Pesach night? This is because there is no extra verse teaching about these.

Rambam (Hilchos Tefilin 4:13): Anyone exempt from Kri'as Shema is exempt from Tefilin.

Rosh (Hilchos Tefilin 29): Even though we hold that Tefilin applies at night, Tefilin does not apply on Shabbos or Yom Tov.

Rambam (Sefer ha'Mitzvos Aseh 159): We are commanded to cease from Melachah on the first day of Pesach.

Sefer ha'Chinuch (Mitzvah 297): One must cease from Melachah on the first day of Pesach. This applies also to women. (The same applies to every Yom Tov.)

Tosfos (Kidushin 34a DH Ma'akah): When there is a Lav with the Aseh, in any case women must do the Aseh to avoid transgressing the Lav! However, if they are exempt from the Aseh, a different Aseh could override the Lav.

Sha'ar ha'Melech (Avodah Zarah 12:3): The Gemara (Sukah 28b) expounds "Ha'Ezrach" to obligate women in Tosefes Inuy (the Aseh to fasting on Yom Kipur). It did not need to use the verse to obligate them in Aseh itself. Since there is a Lav and an Onesh (for eating), we already know that women are obligated in the Aseh. This is like Sefer ha'Chinuch. However, Tosfos (ibid.) disagrees. Perhaps Tosfos learns that the Gemara asked why the Beraisa needs a verse to obligate women in Inuy. They are obligated due to the Lav and Onesh!

Sha'ar ha'Melech Pesulei ha'Mukdashim 19:5 (DH Acharei): Since the Lav of Nosar applies to women, also the Aseh, which is to correct fix transgression of the Lav, applies to them. Mitzvos like Milah and burning Pasul Kodshim apply at all times, just there are times when they are forbidden (Shabbos and Yom Tov). Zeman Gerama is only when there is no Mitzvah at all at certain times, e.g. Tefilin.

Tosfos (Sukah 3a Sof DH d'Omar): Beis Shamai decreed not to sit in a Sukah in which he is prone to be drawn outside. They hold that one who transgressed was not Yotzei mid'Oraisa. We say similarly about one who transgresses Beis Hillel's decrees.

Poskim

Shulchan Aruch (OC 38:3): Women are exempt from Tefilin because it is an Aseh sheha'Zeman Gerama.

Mishbetzos Zahav (1): From Tosfos in Sukah, we learn that if Chachamim decreed not to do a Mitzvah at some times, one who transgressed was not Yotzei, so mid'Rabanan it is Zeman Gerama (and women are exempt).

Pri Megadim Petichah Kelalis 2:14 DH ha'Revi'i: Sometimes women are obligated in an Aseh sheha'Zman Gerama, such as when there is also a Lav.