A Note On Observing Jewish Holidays
All Jewish holidays and observances, with the exception of some fasts, begin on the evening previous to the first day. Except as noted, all require special additional prayers and services are held in the Synagogue.
All Jewish holidays with Sabbath-like restrictions require that all normal business, school or secular activities cease about two hours before sundown on the eve of the holiday to allow for adequate preparations.
Actual holiday restrictions go into effect approximately half an hour before sundown on the eve of the holiday. Some of the restricted activities include all forms of vehicular travel, writing, direct use of electrical devices, measurements and any preparations for, or discussion of, normal weekday activities or responsibilities.
Restrictions end approximately one hour after sundown of the last day. No travel or restricted activities are permitted until then.
Holiday restrictions cannot be relaxed except in circumstances when there is mortal danger to a human life.
Fast days include special prayers and extended synagogue services both in the morning and afternoon. Both food and water are forbidden until approximately one hour after sunset.
Source: Orthodox Union.