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Scientists just voted to redefine how the world keeps time
(www.scientificamerican.com)
This is a most excellent place for technology news and articles.
As you just proved, while it might be possible to write robust software that deals with dates/times, I wouldn't bet on it, and it's Definitely not practical to try.
But you are right that leap seconds were common enough to try and handle. There's a bunch of ways to handle them though, each incompatible with the others.