What is earliest source for MASh"G?
מתני' כל מצות הבן על האב - אנשים חייבין ונשים פטורות. וכל מצות האב על הבן - אחד אנשים ואחד נשים חייבין. וכל מצות עשה שהזמן גרמא אנשים חייבין ונשים פטורות. וכל מצות עשה שלא הזמן גרמא אחד האנשים ואחד הנשים חייבין. וכל מצות לא תעשה בין שהזמן גרמא בין שלא הזמן גרמא אחד האנשים ואחד הנשים חייבין, חוץ מבל תקיף ובל תשחית ובל תטמא למתים:
Mishna (redacted 180-220 CE): All mitzvot for a son by a father, men are abligated and women are exempt. And all mitzvot for a father by a son, both men and women are obligated. And all positive commandments which are time bound, men are obligated and women are exempt. All positive commandments which are not time bound, both men and women are obligated. All negative commandments, whether time bound or not, both men and women are obligated, except for the prohibition of shaving the corners and being impure from the dead.
If women are exempt from a mitzvah, may they voluntarily opt in?
נשים ועבדים וקטנים פטורין מן הציצית מן התורה. ומדברי סופרים שכל קטן שיודע להתעטף חייב בציצית כדי לחנכו במצות. ונשים ועבדי' שרצו להתעטף בציצית מתעטפים בלא ברכה, וכן שאר מצות עשה שהנשים פטורות מהן - אם רצו לעשות אותן בלא ברכהאין ממחין בידן.
Rambam Hilchot Tzitzit 3:9 (Maimonides, 1138-1204, Spain, Egypt, Sphardic)
Women, servants, and minors are not required by the Torah to wear tzitzit. It is, however, a Rabbinical obligation for every child who knows how to dress himself to wear tzitzit in order to educate him to fulfill mitzvot. Women and servants who wish to wrap themselves in tzitzit may do so without reciting a blessing. Similarly, regarding the other positive commandments which women are not required to fulfill, if they desire to perform them without reciting a blessing, they should not be prevented from doing so.
How is it learned/derived that women are exempt from MASh"G?
ומצות עשה שהזמן גרמא נשים פטורות: מנלן? גמר מתפילין. מה תפילין נשים פטורות, אף כל מצות עשה שהזמן גרמא נשים פטורות. ותפילין גמר לה מתלמוד תורה. מה תלמוד תורה נשים פטורות, אף תפילין נשים פטורות.
Gemara: Positive time bound commandments women are exempt. How do we know this? It is learned from tefilin: just as women are exempt from tefilin, so are they exempt from all positive time bound commandments . Tefilin [themselves] are derived from the commandment to study Torah: just as women are exempt from Torah study, so are they exempt from tefilin.
How do we define "Positive Time Bound Commandments"? Here are two approaches.
טורי אבן מסכת חגיגה טז:ב
בני ישראל סומכין ולא בנות ישראל סומכות. הק' התוספות בספ"ק דקדושין (דף לו ע"א) למה לי למעוטי נשים מסמיכה תיפוק ליה דה"ל מ"ע שהז"ג שאין נוהג אלא ביום...ול"נ דלק"מ דלא הוי מ"ע שהז"ג. אלא כל היכא שהזמן הקבוע לה הוא קבוע ועומד בענין כשעבר הזמן אזדא לה לגמרי, ובטלה מצותה, ואין לה תשלומין מעתה. כשופר סוכה ולולב חגיגה
Turei Even - Chagigah 16b (Aryeh Leib ben Asher Ginzburg, c1695-1785, Lithuania, Author of the Sha'agat Aryeh)
Sons of israel perform "s'micha" and ot the daughters of Israel. Tosefot ask the question (Kiddushin 36a), Why do we learn that women don't perform s'micha from a pasuk (exegetical interpretation) when it is a positive time bound commandment (from which women are exempt) since it is performed only in the day?! Because any action which its set time is set and established; when the time passes, the commandment has expired and can't be fulfilled/made up, such as Shofar, Sukkah, Lulav and Korban Chagigah.
Approach #1: If with passage of a specific time frame the precise mitzvah disappears, then is a mitzvat aseh sh'hazman grama. Ex: Lulav for 5775, Matzah for 5775. The opportunity to eat matzah next year is a new/different mitzvah. Temporary suspension of a mitzvah doesn't make it a zman grama. If you don't do a brit milah during the day on day 8, the same mitzvah continues until it is performed. If a woman doesn't do smichah on her korban today, she can do so when she brings her korban tomorrow.
חכמת שלמה אורח חיים סימן תכו
דברכת הלבנה הוי מע שהז"ג ונשים פטורות- וכתב כן בשם השל"ה הקדוש. ולדעתי זה היא תמוה מאד! ואין לו ענין כלל למ"ע שהז"ג, דכלל זה לא נאמר רק במצוה דגוף המצוה שייכא תמיד בכל ענין ובכל זמן; כגון במצה, או סוכה, ולולב וכדומה. דמצוה זו אפשר להתקיים בחשוון כמו בתשרי, ואייר כמו בניסן.
Chachmat Shlomoh Orech Chaim 426 (Rav Shlomo Luria, MaHaRShaL, 1510-1573, Ashkenaz, Lublin, Poland). The Blessing of the new moon is a positive time bound commandment, and women are exempt, and so it is written in the name of the holy Shla'h. And in my opinion this is very surprising! This doesn't pertain at all to mitzvat aseh she'hazman grama; for this rule isn't used except for a commandment in which the action is feasible at all times; such as eating matzah or sitting in a sukkah or holding a lulav, etc. For these commandments can be performed in the month of Cheshvan just as in Tishrei, and in the month of Iyar as in Nissan.
Approach #2: Only a mitzvah which is feasible all year long, but is defined as a mitzvah only by time, is a mitzvat aseh sh'hazman grama. Ex: Sukkah, Matzah. Supported by Ramban. Let's see how he applies this.
חידושי הרמב"ן מסכת קידושין לג:ב
ובמצות עשה שאין הזמן גרמא שייר טובא מורא וכבוד, בכורים, וחלה, כסוי הדם, ראשית הגז, מתנות, ספירת העומר.
Nachmanides/Ramban - 1194-1270, Spain and Israel. (The Gemara left out)...many positive mitzvot that are not time bound, such as fearing and honoring parents, bringing first fruits, challah, covering blood, first shearing of the sheep, gifts for priests, and sefirat haomer.
A mitzvah can have 2 components: Chiyuv Hamitzvah (the obligation to fulfill it) and Kiyum Hamitzvah (the ability to actively fulfill it). Ex: Eidut (providing testimony) - can only be done during the day (kiyum hamitzvah), but the obligation to give testimony (chiyuv hamitzvah) continues through the night. So a mitzvah might be disqualified from being a MASh"G if one of the 2 components don't apply. Which is why a specific verse is used to explain that only men are obligated/allowed to serve as witnesses.
Is there a "nafka mina" or practical difference between these 2 approaches - are there any mitzvot that would be considered a MASh"G by one but not by the other approach?
Other factors: Af hen hayu b'oto hanes - women were included in miracles of Exodus from Egypt, Chanukah, and Purim and therefor obligated in the MASh"G of 4 cups of wine, Chanukah candles, and hearing megilah. These however all rabbinic commandments.