Today (2015-06-30, day with a leap second), the length of a day is 23 times the length of a standard hour, plus the length of the last UTC hour. That's how long a day is, in terms of questions that we are already willing to answer, combined using operations that we understand.
It's also safe to say that someone is more likely to notice a leap second when they happen to ask for a minute spanning the leap second boundary than when they ask for a day spanning the leap second boundary, yet somehow this ambiguity does not prevent us from supporting minutes as a Duration.
Furthermore, quite a few places (Google and Amazon among them, as well as quite a few financial exchanges, according to the article cited above) are smearing the leap second anyway, so actually all our larger-than-second durations at Google (or at Amazon, etc) are slightly wrong today anyhow.
Do we have a better reason than this alleged ambiguity for saying "no"? Pushing the eat-your-antiambiguity-spinach all the way out to the command line seems user-unfriendly.