Friday sundown until Saturday after twilight. A more precise definition would depend upon custom. See also the Related Link.
At the start of the Sabbath.
The Sabbath is ended with the Havdalah service.
The weekly sabbath did end. The "sabbatismos" of God (God's rest) is eternal, and is entered into through faith. The weekly sabbath was a shadow of this rest.
it is always women who start the celebration of sabbath
She lights the Sabbath Candles and says prayers.
Which Jewish ceremony? Bris (circumcisioin)? Havdalah (the end of the Sabbath)? Kiddush (the blessing over wine and bread that starts a Sabbath or festival meal)? Candle lighting (at the start of the Sabbath or a festival)? Tahara (the washing of a corpse before burial)? There are many many more.
It is an expression where you are wishing your fellow Jew a peacful sabbath before the start of the sabbath. Wishing someone to have a peaceful and observant sabbath is the ritual.
at the end of sabbath
it is called rubarb
The Sabbath begins at sunset on Friday and ends at sunset on Saturday.
The sabbath begins at sundown on Friday and ends at sundown on Saturday.
The Sabbath for Seventh-day Adventists starts at sunset on Friday and ends at sunset on Saturday.