Unix keeps the 86400 seconds as an invariant, and ignores the IS size of a second. This should work just fine for negative leap seconds too, you just make your

Unix keeps the 86400 seconds as an invariant, and ignores the IS size of a second. This should work just fine for negative leap seconds too, you just make your seconds shorter instead of longer. Of course, it's a near certainty that it won't work just fine. But it should.