When Org mode prompts for a date/time, the default is shown in default date/time format, and the prompt therefore seems to ask for a specific format. But it will in fact accept date/time information in a variety of formats. Generally, the information should start at the beginning of the string. Org mode will find whatever information is in there and derive anything you have not specified from the default date and time. The default is usually the current date and time, but when modifying an existing timestamp, or when entering the second stamp of a range, it is taken from the stamp in the buffer. When filling in information, Org mode assumes that most of the time you will want to enter a date in the future: if you omit the month/year and the given day/month is before today, it will assume that you mean a future date1. If the date has been automatically shifted into the future, the time prompt will show this with ‘(=>F).’
For example, let's assume that today is June 13, 2006. Here is how various inputs will be interpreted, the items filled in by Org mode are in bold.
3-2-5 ⇒ 2003-02-05 2/5/3 ⇒ 2003-02-05 14 ⇒ 2006-06-14 12 ⇒ 2006-07-12 2/5 ⇒ 2007-02-05 Fri ⇒ nearest Friday after the default date sep 15 ⇒ 2006-09-15 feb 15 ⇒ 2007-02-15 sep 12 9 ⇒ 2009-09-12 12:45 ⇒ 2006-06-13 12:45 22 sept 0:34 ⇒ 2006-09-22 00:34 w4 ⇒ ISO week four of the current year 2006 2012 w4 fri ⇒ Friday of ISO week 4 in 2012 2012-w04-5 ⇒ Same as above
Furthermore you can specify a relative date by giving, as the first thing in the input: a plus/minus sign, a number and a letter ([hdwmy]) to indicate change in hours, days, weeks, months, or years. With a single plus or minus, the date is always relative to today. With a double plus or minus, it is relative to the default date. If instead of a single letter, you use the abbreviation of day name, the date will be the Nth such day, e.g.:
+0 ⇒ today . ⇒ today +4d ⇒ four days from today +4 ⇒ same as above +2w ⇒ two weeks from today ++5 ⇒ five days from default date +2tue ⇒ second Tuesday from now -wed ⇒ last Wednesday
The function understands English month and weekday abbreviations. If
you want to use unabbreviated names and/or other languages, configure
Not all dates can be represented in a given Emacs implementation. By default
Org mode forces dates into the compatibility range 1970–2037 which works on
all Emacs implementations. If you want to use dates outside of this range,
read the docstring of the variable
You can specify a time range by giving start and end times or by giving a start time and a duration (in HH:MM format). Use one or two dash(es) as the separator in the former case and use '+' as the separator in the latter case, e.g.:
11am-1:15pm ⇒ 11:00-13:15 11am--1:15pm ⇒ same as above 11am+2:15 ⇒ same as above
Parallel to the minibuffer prompt, a calendar is popped up2. When you exit the date prompt, either by clicking on a date in the calendar, or by pressing <RET>, the date selected in the calendar will be combined with the information entered at the prompt. You can control the calendar fully from the minibuffer:
<RET> Choose date at cursor in calendar. mouse-1 Select date by clicking on it. S-<RIGHT>/<LEFT> One day forward/backward. S-<DOWN>/<UP> One week forward/backward. M-S-<RIGHT>/<LEFT> One month forward/backward. > / < Scroll calendar forward/backward by one month. M-v / C-v Scroll calendar forward/backward by 3 months. M-S-<DOWN>/<UP> Scroll calendar forward/backward by one year.
The actions of the date/time prompt may seem complex, but I assure you they will grow on you, and you will start getting annoyed by pretty much any other way of entering a date/time out there. To help you understand what is going on, the current interpretation of your input will be displayed live in the minibuffer3.
 See the
org-read-date-prefer-future. You may set that variable to
time to even make a time before now shift the date to
you don't need/want the calendar, configure the variable
 If you find this distracting, turn the display off with