"Empire Time"

The relativity of simultaneity was often cited in the 21st century as reason why synchronized timekeeping across a galactic-scale polity could never truly be carried out. Tremendous precision, at the least, would be needed to keep track of astronomic bodies' relative velocities, time dilation, etc; and time dilation would require that shipboard subjective timekeepers observe different daily schedules from those in slower-moving stationary habitats, while those habitats in turn would experience similar drifts on a smaller scale due to the nature of planetary orbits and galactic proper motion in themselves, throwing off record-keeping of economic transactions or at least, destabilizing the ground beneath Capitalist Age financial speculators. Meanwhile, inability to adequately predict stellar kinematics would make attempts at large-scale precision coordination or even the keeping of accurate starmaps an iffy proposition. How hopeless!
Yet by and large, these complications largely were resolved. Interplanetary and even galactic velocity discrepancies could be corrected for by simple use of twin timekeeping systems for the local and galactic scale, while shipboard clocks would simply be resynchronized once they had re-entered inhabited space - some "jet lag" might ensue, but no major deleterious effects. The first practical wormholes further eased the problem by linking distant star systems directly; wormholes experience time at more or less the same rate on either end, and the shortened distance that signals have to travel greatly eased mutual astrometric tracking across large interstellar polities. Multiversal timekeeping, in turn, benefited from largely the same innovations applied across higher dimensional contexts.
Today in the Mandate Era, the problem of "empire time" is widely considered more or less solved, at least in principle. Certain regions of the Local Nexus do experience disjuncture from common time due to equipment failures, inadequate upkeep or insufficient astrometric capability, but these are technical problems rather than intrinsic ones.