Selichot are special prayers for forgiveness.
• When are they said?
They are usually said on fast days, which are occasions when the Jewish People needs special forgiveness for sin. They are also said during the period preceding Yom Kippur, which is obviously also such an occasion.
In the Sephardic tradition, Selichot are said beginning with the month of Elul, through Yom Kippur.
In the Ashkenazic tradition, they are begun at a time such that there will be ten opportunities for their recitation before and including Yom Kippur. This is based on the custom, once prevalent, that Jews would fast for ten days (eating at night, of course) before and including Yom Kippur.
During the period from and including Rosh HaShanah, through Yom Kippur, there are four occasions when fasting is inappropriate (the two days of Rosh HaShanah, the Shabbat between Rosh HaShanah and Yom Kippur, and the eve of Yom Kippur). Also, because it was felt that a specific day of the week should be identified for the start of the recitation of Selichot, there are two possibilities:
- Motzaei Shabbat (Saturday night) immediately preceding Rosh HaShanah
- Motzaei Shabbat of the preceding week
As far as the time of day on which to say the Selichot, in general, the proper time is the end of the night, just before the morning, since this time is considered, in terms of Jewish Mysticism, a specially favorable time, in terms of the "presence" and "closeness" of G-d.
There are two "however’s" regarding the first night of Selichot. First, it is customary to say Selichos the first night before going to sleep, and, since the first part of the night is considered a time of "din," "judgment," the Selichot are not recited on the first night till after "chatzot," "relative midnight." In New York, because the Season of the Year is Fall and with Daylight Savings Time in effect, this is usually around 1:00 A.M.
Since in the Ashkenazic tradition, Selichot always begins on Motzaei Shabbat, the first prayer begins "At the end of the Day of Rest, we approached You first."