Types and functions for UTC and UT1
 newtype UniversalTime = ModJulianDate {}
 data DiffTime
 secondsToDiffTime :: Integer > DiffTime
 picosecondsToDiffTime :: Integer > DiffTime
 data UTCTime = UTCTime {
 utctDay :: Day
 utctDayTime :: DiffTime
 data NominalDiffTime
 addUTCTime :: NominalDiffTime > UTCTime > UTCTime
 diffUTCTime :: UTCTime > UTCTime > NominalDiffTime
 getCurrentTime :: IO UTCTime
Universal Time
Time as measured by the earth.
newtype UniversalTime Source
The Modified Julian Date is the day with the fraction of the day, measured from UT midnight. It's used to represent UT1, which is time as measured by the earth's rotation, adjusted for various wobbles.
Absolute intervals
This is a length of time, as measured by a clock. Conversion functions will treat it as seconds. It has a precision of 10^12 s.
secondsToDiffTime :: Integer > DiffTimeSource
Create a DiffTime
which represents an integral number of seconds.
picosecondsToDiffTime :: Integer > DiffTimeSource
Create a DiffTime
from a number of picoseconds.
UTC
UTC is time as measured by a clock, corrected to keep pace with the earth by adding or removing occasional seconds, known as "leap seconds". These corrections are not predictable and are announced with six month's notice. No table of these corrections is provided, as any program compiled with it would become out of date in six months.
If you don't care about leap seconds, use UTCTime and NominalDiffTime for your clock calculations, and you'll be fine.
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.
UTCTime  

data NominalDiffTime Source
This is a length of time, as measured by UTC. Conversion functions will treat it as seconds. It has a precision of 10^12 s. It ignores leapseconds, so it's not necessarily a fixed amount of clock time. For instance, 23:00 UTC + 2 hours of NominalDiffTime = 01:00 UTC (+ 1 day), regardless of whether a leapsecond intervened.
addUTCTime :: NominalDiffTime > UTCTime > UTCTimeSource
addUTCTime a b = a + b
diffUTCTime :: UTCTime > UTCTime > NominalDiffTimeSource
diffUTCTime a b = a  b
getCurrentTime :: IO UTCTimeSource
Get the current UTC time from the system clock.