> UTC and POSIX time are adjusted, relative to TAI, to keep the number of seconds in a given day at a nice "easy" 86400
yes, technically POSIX time is defined not as a number of seconds since epoch, but as 86400 * (number of days since epoch) + (number of seconds since last midnight)
yes, technically POSIX time is defined not as a number of seconds since epoch, but as 86400 * (number of days since epoch) + (number of seconds since last midnight)