ISO-8601 Time Standard

ISO-8601 standard was created with the objective of elaborating a crystal clear language to talk about dates and periods and avoid misinterpretation. Here are some tips on possible pattern usage:

• Dates can be defined in format YYYY-MM-DD, with a specific Day, Month and Year. Ex: 2019-04-12, means 12th April from 2019.
• It is also possible to use for example, YYYY-MM, necessarily with “-” in between years and month. Ex: 2019-04, means April from 2019.
• Use -MM-DD, necessarily with two dashes, to represent a day and a month. Ex. -04-12, means 12th April.
• The time is represented in format [hh][mm][ss] or [hh]:[mm]:[ss], defining hours and optionally the minutes and seconds. In this way both 165503 or 16:55:03 are valid time representation for the same moment. [hh]:[mm] and [hh] are both valid time formats; 
• When combining date and time, concatenate both patterns with the letter “T“, determining beggining of the time representation: <date>T<time> . Ex. 2019-10-12T12:15 means 12th October from 2019, exactly at Midday and 15 minutes.
• About midnight: “2019-04-12T24:00” is the same instant as “2019-04-05T00:00”.
• Duration (“how long“) is represented with the format P[n]Y[n]M[n]DT[n]H[n]M[n]S, where n is a number. The letters mean the representation of date and time:  
  • P express that this is a period format, and should be the first character;
  • Y for years; M for months; D for days;
  • T is the delimiter for the time;
  • H for hours; M for minutes; S for seconds;
•  Date or time can be omitted, but always remember to use the P delimiter in the beginning, and if using time, use the T delimiter necessarily. Ex. the duration of two years and four months, and three hours can be represented with: P2Y4MT3H;  A duration of 4 hours and 20 minutes, by PT4H20m; “P3M” is a three-month duration and “PT3M” means three minutes duration;
• The time intervals can be represented with / delimiter,  where we can have:
  • begin/end. Ex. 2019-04/2019-06 to represent from April to June 2019;
  • begin/duration. Ex. 2019-12-25T10:00:00/PT1H to represent the duration of one hour starting at 10 AM from  Christmas day (25th Dec) in 2019.
  • duration/end. Ex. the period that covers three months before 12th October: P3M/-10-12;
  • duration. Ex. two seconds period: PT2S;
• For repeating intervals, the delimiter R is used Rn/<interval>, where n is the number of times the repetition should happen. Unlimited repetition is achieved by ommiting letter n. Examples:
  • Repeat two times, starting at 12th April 2019 Midday.  R2/2019-04-12T12:00;
  • Repeat an interval of 5 minutes, 5 times, before 01th Jan 2020: R5/PT5M/2020-01-01
  • Repeat every 1 hour and 30 minutes: R/PT1H30M