Why does a clock need more features. It tells the time. MAYBE add an alarm to it so you don’t have to have 2 apps. that’s it. It’s not a calendar, it’s not a task-tracker, and the last time I checked we still have 24 hour days.
The only updates it needs are UI updates (which should be system-side anyways) and if the time source changes, which are a few bytes at most.
leap seconds should be handled via the standard sync just like any normal deviation