Starting Shavuos Early

Question: I know that we do not normally daven maariv on the first night of Shavuos until nacht. Can we make an earlier minyan?

Answer: The Shelah (Shavuos 1) states that one must not recite kiddush or begin the Yom Tov meal on the first night of Shavuos until it is nacht (nightfall). As the Torah writes that one must count seven complete weeks of the omer, bringing Yom Tov early would diminish this. The Magen Avraham (494:1) and Pri Chadash (OC 494:1) also write that one must wait until nacht on the first night of Shavuos to recite kiddush.

However, the Yosef Ometz (850) notes that he never witnessed anyone in Germany wait until nacht to recite kiddush. He argues that waiting until nacht reduces the time available for learning on Shavuos night. Similarly, the Korban Nesanel (Pesachim 10:2) states that it is not necessary to wait until nacht to recite kiddush and begin the meal.

The Mishna Berura (261:19; Biur Halacha 261:2) discusses a machlokes about whether the mitzva of tosefes Shabbos, which involves adding time to the beginning and end of Shabbos (Rosh Hashana 9a; Yuma 81b) is miderabanan or mideoraisa. The Avnei Nezer (OC 16:12) argues that the mitzva is mideoraisa and applies equally to bringing Yom Tov in early. Consequently, R’ Yaakov Emden (Siddur Beis Yaakov, Shavuos 4) suggests that in order to fulfil tosefes Yom Tov, one should daven maariv early.

Despite this, the Taz (OC 494:1), Shulchan Aruch Harav (OC 494:2) and Mishna Berura (494:1) all maintain that one should not daven maariv before nacht. R’ Naftali Zvi Yehuda Berlin (Haamek Davar, Vayikra 23:21) explains that the Torah commands Shavuos to be observed 'on that very day', which necessitates waiting until nacht.

In conclusion, it is important to wait until nacht to daven maariv on Shavuos if that is the practice of your kehilla.