Most machines use UTC internally (with varying epoch dates to represent it). And this is absolutely great until you need to interface with meatbags, ie local time. It's not just display of time either: think about anything Cron does in localtime, eg backups or open building door locks, or send an ACH payment file; then ponder all the corner cases of DST switches. Eg do you do something twice, or never? What if you reboot somewhere in the DST switch period? etc. All these shenanigans are dictated by the TZDB.
Oh, and UTC also contains leap seconds.
I don't recall how `cron` and other schedulers handle it, though.
Things either happened twice or never, it was always really painful. In any growth company, I would imagine that these things keep occurring, as people haven't hit the bugs themselves yet.
No, they rally aren't. Most machines use Posix time internally, and the fact that it doesn't reflect real-world leap seconds is a problem.
To be clear, the software perspective is to use Unix time instead.[0]
[0] https://en.wikipedia.org/wiki/Unix_time