[masklinn]

> How does UTC jumping around affect this? If a leap second is removed it doesn't mean you've waited 0 seconds.

No, but it means UNIX time does not advance by exactly one second per elapsed second. Instead it advances by either 0 or 2.

> It's not Unix time doing that. It's UTC.

It's also unix time. unix time is (86400 * days_since_epoch + seconds_since_midnight). A leap second means a day is not 86400 seconds, and thus you'll either get a skip or a repeat on midnight rollover.