That app is much older than a week. I’m seeing last update 4 weeks ago and I’ve had it installed for what feels like a year or so, but might not be that long.

Right there in your link, it says she’s AI:

Amanda Caswell is an AI journalist

/s

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.