Time is one of the fundemental units of physics, defining quantities such as velocities. Numerous races have engaged in the study of space and time, though after thousands of years of study, it is the protoss that possess the greatest understanding and even then, full understanding is limited to the preservers.
Time is not linear. It wraps in on itself, congregating around feelings, moments of history and memories. It then scatters carrying the imprint of these things with it. They attempt to merge, succeed, then scatter again, the process repeating itself into infinity. While the nature of time is constantly shifting and changing, certain patterns emerge in it. One such pattern is the xel'naga's cycle of reproduction which has shaped the history of the universe.
This article or section contains information derived from Co-op Missions, and should not be considered part of the official StarCraft storyline.
Space-time anomalies can emerge large enough to affect entire moons. Kaldir experienced one such anomaly during the End War.
In deep space, keeping track of days and months was close to impossible in isolation, as such it was necessary to track relative time compared to the rotation of major worlds such as Tarsonis and Umoja.