By default, recurring actions are scheduled relative to when the resource started. So if your resource was last started at 14:32 and you have a backup set to be performed every 24 hours, then the backup will always run at in the middle of the business day - hardly desirable.

To specify a date/time that the operation should be relative to, set the operation's interval-origin. The cluster uses this point to calculate the correct start-delay such that the operation will occur at origin + (interval * N).

So if the operation's interval is 24h, it's interval-origin is set to 02:00 and it is currently 14:32, then the cluster would initiate the operation with a start delay of 11 hours and 28 minutes. If the resource is moved to another node before 2am, then the operation is of course cancelled.

The value specified for interval and interval-origin can be any date/time conforming to the ISO8601 standard. By way of example, to specify an operation that would run on the first Monday of 2009 and every Monday after that you would add:

  <op id="my-weekly-action" name="custom-action" interval="P7D" interval-origin="2009-W01-1"/>