[tim--]

This is a misconception. ISO8601 has six versions, is 14 pages long, and defines way to many ways to represent dates and times.

Everyone should follow RFC 3339.

https://www.rfc-editor.org/rfc/rfc3339#section-5.6

[geenew]

Thanks! Wasn't aware of that spec.

[db48x]

But they‘re mostly trivial variations of each other, or durations that nobody uses at all.

[tim--]

That's the problem though. If you don't support the durations that nobody uses, then you can't fully support ISO8601 dates.

Every trivial variation is another if/switch statement.

[db48x]

Durations are not used in places that need a timestamp, and visa versa. More applications need timestamps than need durations.