Universal Universe Time: Subverted. On the one hand, it’s played straight; just about all of the Associated Worlds sync to empire time/weavetime, the consensus establishing-a-common-relativistic-reference-frame timebase agreed to and broadcast by all the stargates – see Microts for more details – so that there’s some agreement with everyone else as to what the time is.
(The Voniensans, perverse as ever, don’t – so life along that border can get confusing.)
But weavetime is mostly of use for scientific purposes and for synchronization. In the Empire, to provide more practical units for daily use, there’s Imperial Standard Time, which is the weavetime-synchronized version of the Eldrae homeworld’s cycles, and so is used there and everywhere else where the local planetary or habitat cycles aren’t convenient, and as the standard commercial calendar; meanwhile, many planets, moons, and habs, on the other hand, have a local calendar based on their own cycles which they use for local purposes. (Or sometimes two, if orbits and seasons are out of sync with each other.) And lighthuggers, of course, have their own version of IST which also include the relevant frame corrections. Not that the other local times don’t include many and various frame corrections, but lighthuggers are where they become really obvious.
Other polities, as expected, do much the same thing internally, establishing their own interplanetary and planetary calendars, synchronized to the weavetime timebase – so even though one does still have to ask what time it is, at least understanding the answer is usually a simple matter of unit conversions.
(Datetimes from anywhere that doesn’t have a local stargate/timebase beacon operational invariably include a +/- estimated-drift figure.)