Parshat Vayakhel begins with the words "Vayakhel Moshe et kol adat B'nai Yisrael.", "Moshe assembled the entire congregation of B'nai Yisrael and said to them: These are the words that God has commanded you to do: Work may be done six days but the seventh day must be holy to you it is Shabbat Shabbaton for God..." (Shmot 35:1).

According to Ramban, The reason why "kol", "all" is used is because it includes the men, women and children who are all obligated in the commandment of Shabbat.

One may have thought that women are not obligated in the positive mitzvot of Shabbat since they are time bound commandments and there is a general rule in the Mishna in Kiddushin that women are exempt from all positive mitzvoth that are bound by time.

The Gemara in Shabbat 20b teaches that women are obligated by Torah law in the recitation of the Shabbat Kiddush. Why is this so? Isn't Kiddush a time bound positive commandment from which women are excused from performing? Rava explained: When recording the Shabbat commandment in Shmot 20:8, Scripture says: Zachor, Remember the Shabbat day and when recording it in Devarim 5:12 it says Shamor, Guard the Shabbat day. This teaches us that these two aspects of Shabbat observance are compared to one another. Whoever is included in the commandment of guarding Shabbat is likewise included in the commandment of remembering it. Therefore, since women are obligated in the mitzvah of shamor (the negative commandment to refrain from the 39 forms of forbidden work), they are also obligated in the mitzvah of zachor (the positive commandment to recite Kiddush).

A similar ruling is taught in the Gemara in Pesachim 43a-b concerning women's obligation to eat Matzah: Rabbi Elazar said: Women are obligated by the Torah to eat matzah as it is written in Devarim 16:3, "You shall not eat chametz with the Korban Pesach sacrifice, for seven days you shall eat matzah with it." Whoever is obligated in the prohibition not to eat chametz is obligated as well in the commandment of eating matzah. Since women are included in the prohibition against eating chametz they are included as well in the obligation to eat matzah.

The general rule in the Mishna in Kiddushin that women are exempt from all positive time-bound mitzvot has many exceptions. There are in fact many positive time bound mitzvot that women are obligated in.

As the saying goes, there are exceptions to every rule!