The leap second mechanism amounts to a collective agreement to rewrite chronological history. It's like a git rebase for your clock. Everyone (almost) in practice does math as if leap seconds never happened, and the consequent divergence from physical time ends up not mattering.
If we add a leap second at the end of 2025, nothing in 2024 gets rewritten. Only the future meaning of pointer expressions like "12 pm on January 2nd 2025" change their value. When I want exactly 48 hours after 12 pm Dec 31, I use a leap second independent time representation. But since usually I want the same thing everyone calls 12 pm Jan 2, I usually use a representation that gives me that.
And I, among many, take meticulous care to do my date math (for a bank core system) only in ways that naturally support leap seconds.
