How to describe time periods

Dates

Dates are specified within Time_Period_Information.
The dates should be written like YYYY (a four-digit year) if you only know the year, or YYYYMMDD (where MM is the month 1-12 and DD the day 1-31) if you know the day.

Times

You can add times too, but don't unless you really need to be that precise. Write the times as HHMM or HHMMSS (HH is hour 0-24, MM minutes 0-59, SS seconds 0-59):
  Single_Date/Time:
    Calendar_Date: A year or day
    Time_of_Day: Time as HHMM or HHMMSS
  Range_of_Dates/Times:
    Beginning_Date: Starting year or day
    Beginning_Time: Time as HHMM or HHMMSS
    Ending_Date: Ending year or day
    Ending_Time: Time as HHMM or HHMMSS