[msla]

And here we have the root of the disconnect between wall-clock time and stopwatch time.

In short: How long it takes to cook an egg doesn't change because someone inserted a leap second.

Of course, when people try to do the obvious thing, and measure time durations using a wall clock, that's when the fun begins. In that world, "a day from now" is not a consistent number of seconds in the future, due to the aforementioned leap seconds, daylight savings time, and, potentially, time zone shifts if the person doing the measuring is traveling, or is (or, perhaps, was) in a particularly "interesting" jurisdiction.