tough: dates with microseconds may be non-compliant

[webern]

What you quoted from the specification might imply that fractions of a second must not be included, but it doesn't say that explicitly.

Spec is explicit about time formats ( this is not linked to from expiry sections but it is in there):

Metadata date-time follows the ISO 8601 standard. The expected format of the combined date and time string is "YYYY-MM-DDTHH:MM:SSZ". Time is always in UTC, and the "Z" time zone designator is attached to indicate a zero UTC offset. An example date-time string is "1985-10-21T01:21:00Z".

This is very clear: timezones and microseconds are not allowed

Originally posted by @jku in #426 (comment)