Using time to sync between computers is one of the classic distributed systems problems. It is explicitly recommended against. The amount of errors in the regular time stack mean that you can’t really rely on time being accurate, regardless of leap seconds.

Computer clock speeds are not really that consistent, so “dead reckoning” style approaches don’t work.

NTP can only really sync to ~millisecond precision at best. I’m not aware of the state-of-the-art, but NTP errors and smearing errors in the worst case are probably quite similar. If you need more precise synchronisation, you need to implement it differently.

If you want 2 different computers to have the same time, you either have to solve it at a higher layer up by introducing an ordering to events (or equivalent) or use something like atomic clocks.