If I say something like "I had to catch a 6am flight", that means something to you without knowing what time zone I'm in. Absolute and relative times are both useful.
> If I say something like "I had to catch a 6am flight", that means something to you without knowing what time zone I'm in.
But it's really meaningful only in the sense that it's early morning, so that the same information could be conveyed by saying "I had to catch an early-morning flight." (More precise information than that could always be conveyed: "I had to catch a flight 1 hour before sunrise", or whatever.)
