Btukfyl

I had an argument with a friend about when you can perform the Pesach seder mitzvot of eating a kezayit of shmurah matzah and drinking four glasses of wine (beginning with kiddush).

My friend said that you must wait until after sunset to say kiddush and eat the kezayit of matzah since these mitzvot remind us of the exodus from Mitzrayim. Therefore, these mitzvot must be performed at the time the Jews left Egypt, after sunset following the day of the 14th of Nisan.

I said that this is true, unless you choose to bring yom tov in early (earlier than sunset). I rationalized that, just as with Shabbat, once you bring in yom tov, you can perform kiddush (even if before sunset). And, when you get to the part of the seder to eat Matzah, you can also fulfill this obligation as well.

So the question is, if you choose to bring in yom tov early, do you still have to wait until sunset to start the seder and say kiddush (fulfilling the obligation of drinking the first of the four cups of wine)? Similarly, if you bring in yom tov early, do you nevertheless have to wait until sunset to eat matzah?

You cannot begin to recite Kiddush, drink 4 cups and eat matsa and maror before the night (exit of the stars, later than sunset). The time the Jews left Egypt was at night. And the korban Pesach and matsot were eaten at night. Further eating of pesach dorot was established by Tora as a night mitsva.

Shulchan Aruch Orach Chayim 472.1

אבל לא יאמר קידוש עד שתחשך:‏

One doesn't say Kiddush until it gets dark.

Mishna Berura

(ד) אבל לא יאמר קידוש - ר"ל דלא תימא כיון שמצוה למהר יתחיל הקידוש וההגדה מבעוד יום כמו שמצינו בשבת ויו"ט שיכול להוסיף מחול על הקודש ולקדש ולאכול מבעוד יום וכנ"ל בסימן רס"ז קמ"ל דלגבי פסח אינו כן לפי שאכילת מצה הוקשה לפסח שנאמר על מצות ומרורים יאכלוהו ופסח אינו נאכל אלא בלילה והקידוש צריך להיות בשעה הראויה למצה ועוד דכוס של קידוש הוא אחד מארבע כוסות וכולהו בתר הגדה ומצה ומרור גרירי: ‏

Regarding Pesach, because eating matsa is linked in the verse to Pascal sacrifice. The verse says that they must to eat it with matsot and maror. And pesach is eaten only by night. And Kiddush needs to be at a time adapted to eating matsa. Additionally, the Kiddush cup is one of the four cups and all 4 cups follow hagada, matsa and maror.

See also Aruch Hashulchan