So. How do I compensate for this if I wish to convert a milliseconds since epoch value to an accurate datetime type? Are these the concerns that smart people who write DateTime types in frameworks deal with?
Leap years and leap seconds are required due to other effects that don't (leap years because of the non-integer ratio between year length and day length and leap seconds because the length of day is increasing slowly)
We disabled leap-seconds at work in our NTP servers, and just use the normal mechanisms to compensate slowly.