Couple things to know about leap seconds, which have ceased to be as of this week:

* Unix timestamps are defined as seconds since epoch minus however many leap seconds have happened so far (!)
* There have been 27 leap seconds, with the last one in 2016.
* Negative leap seconds were a possibility and could have broken everything. No more.

https://www.bipm.org/en/cgpm-2026/resolution-5

https://old.reddit.com/r/programming/comments/1x6uhya/bipm_announces_the_end_of_leap_seconds/pgylixh/

https://en.wikipedia.org/wiki/Leap_second