I just specify the time zone along with the 02:30 and that ambiguity goes away. Eastern Time here, so 02:30 EDT is different from 02:30 EST, by an hour of course.
My big worry is how to express that in seconds since the start of time (presumably the Big Bang). So if the estimate of when the Big Bang happened is wrong, I have to adjust all my absolute time clocks. And then there’s the stretching of time from relativity theory due to acceleration and gravity. Makes 02:30 look easy!