That would be an ... interesting ... number of pieces. (0, in Unix internal timestamps, is Jan 1, 1970, 00:00 UTC).
It was January 1, 1970 at 00:00:00 UTC. The epoch moves every time a leap second is added to the UTC time scale.
Using UTC instead of TAI (GPS didn't yet exist) was a major mistake. Don't get me started...
Never thought of that; but of course it would.
Time/date manipulation, on computers, is harder than most people -
including all too many developers - realize, especially as as soon as time changes enter the picture (you aren't even safe in a single time zone, if that zone has daylight savings - or ever changed in the past).