I didn't say aliens would care about UTC, did I? I said that we would have to specify a point in time without resorting to calendars. I didn't say we would use offset to UTC, because aliens don't know UTC either. But presumably they can measure time, so we could e.g. measure a point in time as an offset to "now". We would also have to use units that they understand. Not seconds, but perhaps Cesium revolutions.

> And it seems a bit pedantic to separate it

I would say that the fact that you can't see a distinction between time and a calendar is precisely the reason you're confused. So I wouldn't consider it pedantic.