Nights in Mafia are the phases between days when all players submit their night actions. Each night ends at a time determined and announced by the host, who publishes a night post. Most of the actions in a Mafia Game are actions that can only be submitted during the night via PM or in faction BTSC. A night may be ended early by a host, if all players mark their actions as final (usually using the red color for final actions).
It should also be noted that game days and nights do not refer to any real-world time. Typically, nights and days are each 24 hours and are not dependent on any real-world time zone.