This is the simplest representation of UTC. It consists of the day number, and a time offset from midnight. Note that if a day has a leap second added to it, it will have 86401 seconds.
addUTCTime a b = a + b
diffUTCTime a b = a - b
Convert a ToD in some timezone to a ToD in UTC, together with a day adjustment.
converts an internal clock time into a CalendarTime in standard UTC format.