A timestamp may be preceded by special keywords to facilitate planning:
On the deadline date, the task will be listed in the agenda. In
addition, the agenda for today will carry a warning about the
approaching or missed deadline, starting
org-deadline-warning-days before the due date, and continuing
until the entry is marked DONE. An example:
*** TODO write article about the Earth for the Guide DEADLINE: <2004-02-29 Sun> The editor in charge is [[bbdb:Ford Prefect]]
You can specify a different lead time for warnings for a specific
deadlines using the following syntax. Here is an example with a warning
period of 5 days
DEADLINE: <2004-02-29 Sun -5d>.
The headline will be listed under the given date1. In addition, a reminder that the scheduled date has passed will be present in the compilation for today, until the entry is marked DONE, i.e., the task will automatically be forwarded until completed.
*** TODO Call Trillian for a date on New Years Eve. SCHEDULED: <2004-12-25 Sat>
Important: Scheduling an item in Org mode should not be understood in the same way that we understand scheduling a meeting. Setting a date for a meeting is just a simple appointment, you should mark this entry with a simple plain timestamp, to get this item shown on the date where it applies. This is a frequent misunderstanding by Org users. In Org mode, scheduling means setting a date when you want to start working on an action item.
You may use timestamps with repeaters in scheduling and deadline
entries. Org mode will issue early and late warnings based on the
assumption that the timestamp represents the nearest instance of
the repeater. However, the use of diary sexp entries like
<%%(diary-float t 42)>
in scheduling and deadline timestamps is limited. Org mode does not
know enough about the internals of each sexp function to issue early and
late warnings. However, it will show the item on each day where the
sexp entry matches.
 It will still
be listed on that date after it has been marked DONE. If you don't like
this, set the variable