 Nightfall (צֵאת הַכּוֹֹכָבִים, "Tzet Hakochavim") is described in detail above.After nightfall, it is considered definitely the following day.All restrictions of the previous day go away, and any Mitzvot that must be performed at night (such as the evening Shema, the Seder, or Bedikas Chametz may be performed.