Timestamps and scheduling guides
Leap seconds: Unix time and RFC 3339 acceptance
Distinguish the leap-second notation allowed by RFC 3339 from the date subset accepted by JavaScript tools.
Recognize second 60
RFC 3339 permits a second value of 60 at an actual positive leap second under its rules. It is not valid at an arbitrary minute.
A broad standards grammar can therefore accept forms that ordinary date libraries do not implement.
Historical leap-second notation:
2016-12-31T23:59:60ZCheck the runtime subset
JavaScript Date does not represent leap seconds as distinct second-60 instants. The historical string above is rejected by common Date parsing.
Nav Tools is not a leap-second-aware astronomy or timekeeping library; treat such input as outside its ordinary timestamp workflow.
Unix time is not a leap-second counter
Conventional Unix/POSIX time treats days as 86,400 seconds for its time representation and does not provide a unique accumulated leap-second count.
Systems can step or smear clocks around leap seconds. Cross-system measurements need the actual clock policy, not only an ISO timestamp.
Preserve the source notation when needed
For a feed that explicitly carries leap seconds, preserve the original text and use a library with the required time scale and leap-second data.
Do not silently rewrite second 60 to second 59. That changes meaning and can merge distinct events.