Sometimes I have wondered is there proper write up of how messy intragalactic or intergalactic communications and time keeping would be. With or without FTL com

Sometimes I have wondered is there proper write up of how messy intragalactic or intergalactic communications and time keeping would be. With or without FTL communication... Relativistic effects could actually be significant. Not to mention different rotation rates, day lengths, month lengths and so on... Leap seconds are comparatively simple problem...