IIRC the more serious proposals for a global time scheme deliberately abandon the old 24:60:60 so that daylight expectations, locally as they would be, would have to be re-learned anyways. Up to that point that doesn't sound that bad to me. But where i don't see any chance is durations, how many seconds/minutes/hours. I suspect that a change to duration units would be even harder to adapt to than metrification of lengths.