Shabbat and the biblical holidays, known as chagim, are observed for a duration of 25 hours instead of the typical 24 hours. Note that these are halachic hours, measured as a twelfth the time from sunrise to sunset, so its slightly shorter in the winter etc.. This additional hour is called “tosefet Shabbat” or “tosefet yom tov,” meaning the “addition of Shabbat” or the “addition of the holiday.”
The concept of extending the length of these holy days is rooted in Jewish law and tradition. It serves as a way to elevate and sanctify the transition between the ordinary days of the week and the sacred time of Shabbat or the holiday. Moreover, by adding this extra hour, Jewish individuals ensure that they refrain from any activities that may unintentionally infringe upon the sanctity of these special days. It acts as a buffer, providing a clear distinction between the mundane activities of daily life and the unique observance and atmosphere of Shabbat or the holiday.
This practice of extending the holy days is consistent across all biblical holidays, including Pesach (Passover), Shavuot, Rosh Hashanah, Yom Kippur, Sukkot, and Simchat Torah. Tosefet Shabbat and tosefet yom tov is to emphasize the significance of these special occasions, allowing individuals to fully immerse themselves in the observance, prayer, study, festive meals, and communal activities associated with Shabbat and the holidays.
It is important to note that the exact timing of when tosefet Shabbat or tosefet yom tov begins and ends will vary based on geographical location and local customs as to when the times measured from solar cycles is. Therefore, it is advisable to consult with your local Jewish community or rabbi to determine the precise timing for observing Shabbat and the holidays in your area if no such calendars are available. When in doubt, when 3 stars are visable in the night sky, the week has begun.
By embracing the extended duration of these holy days, Jewish individuals have the opportunity to elevate their spiritual connection, create a distinct atmosphere of holiness, and fully immerse themselves in the joyous and meaningful observance of Shabbat and the biblical holidays.