[nulagrithom]

I don't understand this one:

> If I wait exactly one second, Unix time advances by exactly one second

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

I feel like this is wrong too:

> If there’s a leap second in a day, Unix time either repeats or omits a second as appropriate to make them match.

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

[seaish]

Unix time is based on a hard calculation of UTC seconds, minutes, hours, days, and years. So UTC jumping causes a discontinuity in Unix time.

Im pretty sure the second graph is mislabeled (the UTC second after 23:59:60 should be 00:00:00), but Unix time takes 23:59:60 to mean the same as 00:00:00. So 23:59:60.5 is also the same as 00:00:00.5, and so on. If you parsed the Unix time into a readable timestamp, it would tell you it's the first second of the next day for two seconds.

[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.

[jlg23]

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

The OP did not make this claim. He said that waiting 1s does not necessarily increase the Unix time by one second - not the other way around.

Or how my highschool math teacher put it: Every time it rains, the street gets wet. But not every time the street is wet, it rained - maybe my dog just took a leak....

[Groxx]

UTC jumping around affects it if you're basing your time-elapsed measure by checking "time.now() - previouslySavedTime". That can give you a negative value, if e.g. your 1/2-second elapsed time crossed a leap second.