The Jewish calendar and Jewish holidays are guided by the variation in the manner in which the days are reckoned. In most other parts of the world, a day is reckoned as the period from midnight to midnight. But, for the Jews, the day denotes the period from sunset to sunset. For this reason, Jewish holidays will commence at the sunset of the day prior to the holiday mentioned in the Jewish calendar. Similarly, the holiday would end with the sunset on the date mentioned in Jewish calendar for the particular Jewish holidays.
The Jewish Holidays
To understand the precise timing of Jewish holidays, you should consult a Jewish calendar or the Chabad or Orthodox Union closest to you. No work is permitted on some of the Jewish holidays and these include Rosh Hashanah, Shemini Atzeret, Simchat Torah Shavu'ot and Yom Kippur. Similarly, the first two days of Sukkot, the first two days, - the seventh and eight day, of 'Passover' are also prohibited days for work