Ah, Dwarmin, you make me very happy. That Chronicle was gold.
So, as far as dates go, that's one of those little uncertain things that changes everywhere and is only united by the need for interstellar trade.
The common terms of time are the second, minute, and hour, all based around the cesium atom. (One second corresponds to 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom) Day, however, is the beginning of the uncertainty.
Every world runs, as one would imagine, on a different 'day'. One day often, but not always, corresponds to one solar cycle. Each of those days are typically on a calendar that is seasonal (unique to the planet) or imperial (unique to the empire). Now, if the calendar is imperial, that means the year is imperial, and thus unifies the concept of year across one empire. However, if the calendar is seasonal, then the concept of year is individual, and typically represents a counter started from the time it was colonized. (Again, not always) Worlds that do not have a day/night cycle, such as colonies occupying the habitable belt of a tidally locked planet, either use some sort of arbitrary interval determined at the time of foundation or resort to more outlandish measures for determining the concept of day. Space stations, deep space colonies, underground civilizations, all of these have to run some concept of time, and, in many cases, it is more efficient to run an individualized concept of time. While this can make the interface between worlds rather grating, and is a staple of modern cinema for both drama and comedy, it is typically locally efficient.
However, 'locally efficient' doesn't cut it for interstellar work. There, a unified system of time is needed. Deals on the galactic market REQUIRE time to be unified across wildly disparate expanses of space. While relativity can occasionally be a pain and actually distort relative time, the galactic market is still the primary source of what might be considered a universally accepted time. Interestingly, however, the mechanism for keeping constant time was more discovered than invented by the merchants. The Deep, the galactic scale information network containing everything from pornography to advanced warship design specs, is a computer system that demands synchronization. While it is unlikely that even the most masterful legion of programmers could enforce a time, the Deep is made up of countless adaptive algorithms designed to 'learn' how to interface with one another- the only viable process when attempting to access a database that contains information across millennia, stored by countless forgotten empires. The requirement for synchronization across the Deep, and the truly freakish adaptability of the medium itself, creates a universal system clock that is capable of being used across the Deep. There is no information on when this clock started, and there is no information on when it will flip over, but it does allow for a universal concept of time.
The ability to compute a number that represents the present, and a number that represents the feature, and from those two numbers deduce a number of seconds, minutes, and hours between the two, is one of the principal reasons that an Empire must be able to utilize the GMS framework before it can be considered prime-tech. Without it, time is local and meaningless. However, that being said, while one could work out the number of hours that have based since the Deep clock began counting (3.154e+8 | 0.3154Gh), this gives no notion of 'year' or 'date'. The Deep clock gives no notion of true beginning, only the number of milliseconds that have passed since an arbitrary point in time. While this number might have enough backing to be capable of increasing until the universe ends, it is likely that it has an upper bound, after which point the clock will reset and begin counting from 0 again. There is no way of knowing when that will happen, or how many times it has happened in the past.
The present is a number. Set points in the present can likely be defined by a number (assuming they do not exceed the reset value), and times up to 3.154e+8 hours in the past can be defined by a number. The relationship between those numbers is useful for the stabilization of a galactic time, but there is no intrinsic meaning to it.
Make sense?