The Mishna Berura writes in siman תצ״ד that we wait till tzais hakochavim before we daven maariv the night of Shavuos, in order to make sure that we have full 49 days of sefirah – תמימות. Many Achronim question this psak. As the Yaavetz writes in his siddur, the source for this stringency of not being able to daven early is the Taz, and yet the Taz himself writes in Hilchos Sukka that once a person accepts Yom Tov early, they have turned the day into night, and if so there should be no problem doing so on Shavuos night as well.
If we investigate the history of this debate, we find nothing in the Gemara or the Rishonim that implies that we can’t make kiddush, and certainly daven early for Shavuos. The main source starts in the 16th century, when the שו״ת משאת בנימין writes not to make kiddush before tzais. Based on his concept, the achronim don’t allow even davening before tzais. And as I said, the Yaavetz and many others have difficulty with this psak.
One famous Rav who was close in time to the משאת בנימין, the author of יוסף אומץ, quotes this minhag from Rav Yakov Falk and he says that he never saw any of the great distinguished rabbis of his time observing this minhag.
The custom today is to wait till tzais to daven and then make kiddush; however, based on the above, many great poskim like Rav Ovadya and Ashkenzic poskim permit making kiddush before tzeis when needed, such as in areas where the night is very late, and certainly one can be maykil in nursing homes.
Although there are other attempts to resolve this puzzle, I want to suggest my own answer to the contradiction in the words of the Taz. Since the days of sefirah are designated to purify and cleanse our middos, then every second of each day of sefirah is precious, and is needed in order to be ready for Shavuos. Therefore, although technically you can accept Shavuos early, but if you do so, you will be missing a few minutes of the days of sefira, and the lesson is as Chazal say, יש קונה עולמו בשעה אחת you can acquire your life in one minute.
by Rabbi Daniel Coren
