UTCTime package:time-compat
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.
ISO 8601:2004(E) sec. 4.3.2
Convert a time of day in some timezone to a time of day in UTC,
together with a day adjustment.