I believe that a realistic answer to this will heavily depend on your universe's current understanding of human sleep patterns. Historical records indicate that prior to the easy access to artificial lighting, people used to sleep in two, 4-hour chunks, separated by a waking period of 1-2 hours. A psychiatrist's experiment in the 1990s confirmed this pattern. One study indicated that access to artificial light has shortened our sleep periods by about an hour; seasons also caused variation.
The best long-term case studies that I know of for someone living in a completely artificial light environment occurred over a period between 1962-1972 by the French scientist <PERSON>. In 1962, he spent two months in a cave, notably without access to a clock or calendar, in an attempt to determine what natural biorhythms would develop in such an environment. In 1972, he repeated the experiment, staying in a cave for six months. For those interested in reading more, the latter experiment was covered in the March 1975 issue of National Geographic in a piece entitled "Six Months Alone in a Cave" (summarized here).
Physiological effects included:
* developing an extended 25-26 hour sleep/wake cycle, with some occurrences of a 48-hour sleep/wake cycle (36 hours awake, 12-14 hours asleep)
* a subjective experience of the passage of time; he experienced it ~2x slower than it was in reality (from the 2-month experiment)
There have also been other experiments done as test runs for living in space habitats. 551
The Russian MARS-500 isolation experiment between 2007-2011 simulated a 105-day stage and later a 520-day mission; it's assumed that this closed habitat had no access to natural light. The data on physiological changes is sparse, but articles indicate that circadian rhythms were effected, and that in general, astronauts are plagued by sleep issues.
What do we do with all these facts?
You'd need have some semblance of conformity to a natural sleep cycle unless you want your residents chronically fatigued, irritable, etc. There would be natural limits to wake periods due to physical exhaustion, of course (if we're ignoring biomedical enhancements or pharmaceuticals).
Shift systems might be based on the length of an orbital cycle, if the artificial environment is orbiting a planetary mass. This could be merely for convenience's sake, if the station is coordinating with people working on the planet who are subject to a more traditional day/night cycle.
Material resources are also a consideration; in <PERSON> recent science fiction novel Seveneves, he posited that staggering wake/sleep cycles across a space station's population would prevent a strain on life-support systems and allow it to support a larger population. This did allow for some overlap between people on different "shifts", for work collaboration & social interaction. Special attention was paid to being cognizant & respectful of seeking someone's attention during their sleep period. In your universe, this could be imbued via the development of cultural practices and the implementation of shared calendar/contact systems that warned someone if they were trying to digitally interact with a person who was in a sleep period. 551