[haberman]

Why would you ever care about leap seconds when calculating the number of days between timestamps? Leap seconds are necessary to calculate the exact number of seconds between two timestamps. But a day isn't exactly 86,400 seconds on leap second days, it's a little bit longer. So the simple algorithm for calculating the number of days between timestamps (floor((ts2-ts1)/86400) seems more correct than anything that takes leap seconds into account.

[Tloewald]

A leap second only lengthens one day.

In any event POSIX time stamps are fine w.r.t. leap seconds, it's the conversion functions which may or may not reflect them.