A duty shift was the portion of the day that various scheduled personnel aboard a starship or space station were on duty. Officers were expected to report on time for their duty shifts and those that failed to do so, without a good excuse, could face penalties such as being placed on report. (TNG: "Hollow Pursuits") Seven of Nine once commented that crewmen Boylan and White were frequently late for their duty shifts. (VOY: "Bliss")
Duty shifts could be exchanged or bartered to some extent. On board USS Voyager, for instance, Neelix once wagered The Doctor three duty shifts in his kitchen for three in sickbay in a shell game. (VOY: "Live Fast and Prosper") Similarly, Odo once assumed a Starfleet security officer's shift aboard Deep Space 9, in order to stand personal watch over First Minister Shakaar and Kira Nerys. (DS9: "Crossfire")
For a brief period of time while Captain Edward Jellico was in command of the USS Enterprise-D in 2369, the ship was put on a four shift rotation. Each shift was designated by a Greek letter: Alpha, Beta, Gamma, and Delta. Though it was difficult for the Enterprise crew to adjust to the new system, none reacted as though it were something Jellico had personally invented. (TNG: "Chain of Command, Part I")
Deep Space 9 was initially put on a three-shift rotation when the Federation took over its administration, but this changed in 2372 due to innovations by Major Kira Nerys. Kira first revealed her plans to Captain Benjamin Sisko when he was seriously injured. She'd hoped that discussing station business might keep him conscious. Later, after he'd recovered, Sisko decided to put the station on a four-shift rotation, saying that the idea had "occurred" to him. He thought the crew "might appreciate more flexibility in their schedules". (DS9: "Starship Down") The concept went through a probationary period until it was finally made permanent because, as Kira put it, there were "less mistakes due to fatigue". (DS9: "Accession")
The day shift or day watch is the first duty period which theoretically happens during whatever would be considered day in space. It takes its roots from day shifts currently in use in military and other jobs. The day shift would presumably be followed by the night watch, which was a time of limited activity. (TNG: "Data's Day", "Lessons")
Commander William T. Riker usually commanded the first bridge shift of the day watch, known as alpha shift. (TNG: "Data's Day", "Rightful Heir", "Lower Decks") In 2367, Worf was in command during the final shift of the day. (TNG: "Data's Day")
The swing shift is a duty shift that is after the day shift, but before the night shift. Crewmembers of Deep Space 9 who were on the swing shift included Whatley, Duarte, Abdon, Nori, Tekoa and Rom. (DS9: "The Assignment")
The night shift is a duty period that occurs during the hours in which an officer would otherwise be sleeping. It is usually relegated to the junior officers, as most people are not fond of the night shift. Aboard starships and space stations, however, there is technically no such thing as "night" or "day". The night shift is preceded by the swing shift. (DS9: "The Assignment")
On the Enterprise-D, this shift was known as night watch, in contrast to day watch. Lieutenant commander Data was often in command of the bridge during the night watch, as he did not require sleep. (TNG: "Data's Day", "Lessons", "Rightful Heir") Doctor Beverly Crusher has volunteered at times for the night shift, as she did in 2370 while Data was away on a mission. She explained that she liked doing this to refresh her starship operations management skills. (TNG: "Thine Own Self")
After Rom resigned from his position of Assistant Manager of Policy and Clientele at Quark's in 2372, he joined Deep Space 9's engineering crew and was assigned to the night shift. (DS9: "Bar Association") In early 2373, Miles O'Brien arranged to have him transferred from the night shift to the day shift. (DS9: "The Assignment")
Ensign Harry Kim served as Voyager's commanding officer during the night shift, twice a week. (VOY: "Night", "Warhead", "One Small Step", "Renaissance Man", "Author, Author") Ensign Jenkins also served as a night shift navigation officer aboard Voyager. (VOY: "Warhead")
Alpha shift was a duty shift aboard the USS Enterprise-A and the USS Enterprise-D, the first shift of the day watch. Aboard the Enterprise-A, the shift began at 0800 and ended at 1600 hours. Aboard the Enterprise-D, it ended at 1200 hours.
In mid-2370, Commander William T. Riker served as commanding officer of the alpha shift. Lieutenant Commander Data served as operations officer, Lieutenant Worf as tactical officer, and Ensign Sam Lavelle as flight controller. Ensign Sito Jaxa was the relief tactical and ops officer. (TNG: "Lower Decks")
Beta shift was the second duty shift of the day watch on board the Enterprise-D, beginning at 1200 hours.
In mid-2370, Commander Riker apparently served as commanding officer of the beta shift, continuing from alpha shift. Other officers on duty at this time included Lieutenant Jae and Ensign Gates. (TNG: "Lower Decks")
Gamma shift was the third duty shift on board the Enterprise-D.
Lieutenant McDowell was part of the gamma shift on board the ship in 2369, until Captain Edward Jellico ordered to rearrange the duty shifts and let the new delta shift replace the gamma shift. (TNG: "Chain of Command, Part II")
In 2370, during a training simulation, Commander Riker informed the alpha shift, including Lieutenant Commander Data, and the ensigns Sito Jaxa and Sam Lavelle, that their response time was seven percent slower that the response time of the gamma shift. (TNG: "Lower Decks")
Delta shift was the fourth duty shift on board the Enterprise-D in 2369.