[paulddraper]

No.

That'd be like saying some points in time that don't have a ISO 8601 year. Every point in time has a year, but some years are longer than others.

If you sat down and watched https://time.is/UTC, it would monotonically tick up, except that occasionally some seconds would be very slightly longer. Like 0.001% longer over the course of 24 hours.

[schneehertz]

The positive leap second of UTC is inserted at midnight, resulting in 86,401 seconds on that day. Reference: https://en.wikipedia.org/wiki/Leap_second