It does. You've been misinformed.
[Edit] wait, Wikipedia contradicts what other people have told me. It doesn't cite sources though.
Would you prefer if I used the article's term of "precise time"?
At any rate, it's a lot better to use precise time timestamps, as a single integer of seconds/miliseconds/vibrations of a caesium atom>, than a dumb "01/01/99" string of integers that rolls over and breaks at Y2K. (with associated fun parsing bugs)
No, it is not always better. If you want to store when a contract is going to end you don't want care how many milliseconds are between now and then. You care that it happens exactly at midnight of the last day of the year. Not an hour earlier or later. Even when politicians intervene between now and then.
If you can't establish accurate precise time, you have no ability to handle all that political crap layered on top. You're trying to solve a top-of-stack problem in the bottom-most layer.
Look at the tz database, the way in which the problem you think needs to be solved is actually handled. It implements all your mushy ever-changing political end-of-day end-of-week crap as a table of conversions to precise-time seconds.
https://en.wikipedia.org/wiki/Unix_time
"Unix time is a date and time representation widely used in computing. It measures time by the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970, the Unix epoch, without adjustments made due to leap seconds."
Unix time does not include leap seconds or other adjustments.