Why are women obligated to say over the story of pesach on pesach if its a time bound mitzva? By matza there is a special derasha used. and the other mitzvos are Rabbinical, so you can say since they were involved in the miracle. But by maggid its a torah mitzva which is time bound.
The source of the obligation for women to say the Haggadah is from the Talmud in Pesachim 108a, which says that they are obligated in the four cups because they were part of the miracle.
Although according to the Rashbam (Pesachim 117b) and the Meiri, the cups are an independent matter to show freedom, and therefore there is no clear derivation that women are obligated in the Haggadah, Tosfos (Sukkah 38a מי שהיה) says that the cups are there in order to say Hallel and the Haggadah on them. In other words, if they are obligated to drink the cups, it is because they are obligated in what the cups are connected to - Hallel and the Haggadah (See חידושי הגרי"ז פ"ז חו"מ הלכה ז).
The Rambam (7:6) and the Rif have a different approach, which according to Rav Chaim Brisker is that there are two obligations in drinking the cups - freedom and as a cup of blessing on what is said on them. So again, from here women are obligated in both aspects of the cups.
Shulchan Aruch (472:4) says women are obligated in everything of the night, which, as the Mishna Brurah (:45) explains it, includes the Haggadah. The Ramo (473:6) says that the Haggadah should be translated so that women and children understand it. The Mishna Brurah (:64) explains again that the women are obligated to say the Haggadah.
The reason for the obligation is that "they were also part of the miracle." [This point is explicitly made in Shulchan Aruch HaRav 472:25]. The Rashbam (Pesachim 108b) explains that the miracle was in the merit of the righteous women, and in their merit all of Israel was saved. Tosfos (Megilah 4a) argues (because the word "also" implies something secondary - Sefas Emes Megila 4a שאף הן) and says that they were saved together with the rest of Israel.
It is a Machlokes Rishonim if the reason of "they were also part of the miracle" can mean that they have a Torah obligation, or if that reason is only enough to say the obligation is Rabbinic. The Pri Megadim explains the two answers of Tosfos (Megilah 4a שאף הן) to why the Gemara learns that women are obligated in Matzah from a Posuk when there is the reason of "they were also part of the miracle" differ on if the obligation is from the Torah or is Rabbinic.
Not to get sidetracked into the details of why, but some limiting principle needs to be applied to when this reason creates a Torah obligation.
It is limited to when women were saved as part of the miracle (so there is no obligation to sit in a Sukkah, even though they were protected by the clouds in the Midbar - מהר"ם ב"ר ברוך ח"ג סימן תעג עמ' סו).
If the Torah explicitly exempts women, this reason can't obligate them (so Sukkah and Tefillin [which are connected to the Exodus] have explicit exemptions associated with them - דבר שמואל להרה"ג רבי שמואל אליעזרוב זצ"ל פסחים קח, ב על תוס' ד"ה היו באותו הנס).
This only applies when the Mitzva involves telling over the miracle (מרומי שדה להנצי"ב מגילה ד, א ד"ה שאף היו - this opinion is explain at length by Rav Yosef Beir Soliveitchik in מבית מדרשו של הרב עמ' יא. מסורה חוברת ב,תשנ. וברשימות שיעורים סוכה עמ' יא.
Another approach to say that this is a Torah obligation comes from the Maraham Shik on his book on the 613 Mitzvos (Mitzvah 21, #2) - because it is a branch of the Mitzvah of Matzah. Since women are obligated in Matzah as learned from a Posuk, and Matzah is called Lechem Oni in this very posuk - and Rashi says (Pesachim 36a) that this means complete hallel and say on it the Haggadah.
Another approach to say that this is a Torah obligation comes according to the commentary of Rav Y. P. Perlow on Sefer HaMitzvos from the Rasag (Part 1 pg. 31) where he explains the Ramban's opinion (Kiddushin 34a) that Sefiras HaOmer is not a time bound positive Mitzvah - because the Torah doesn't say "on this and this day of Nissan" count the omer. Rather it attaches it to the Omer, which is in turn attached to a specific time. Similarly the Haggadah is said at the time of בעבור זה - when there is the obligation of the Pesach, Matzah and Morror.
However according to the Chayei Adam (Hilchos Pesach 130:12) and implied in the Shulchan Aruch HaRav (472:25) as explained by the Lubavitcher Rebbe (Haggadah Shel Pesach סימן מגיד), the obligation is, in fact paskened to be Rabbinic.
Sources for this answer are quoted from הגדה כחלכה by הרב יסוף יצחק כ"ץ.