I have not attempt to do this but have wondered the same thing. I imagine it is possible to do this if you can monitor something that will consistantly generate a achange that can be detected and alerted on. The ...\IDS\log\SISIDSHearbeat.ini file may be a good candidate for this. The "ids.service.updatetime=" value in the file should always be updated every 5 min (or whatever the heartbeat is set to). A filewatch rule that polls the file twice a day should do it. Again, I have not done this just a theory.
You could also get fancy by working with on of the following Datetime paramters types:
datetimevalue: Specify a date and time. The value is based on an agent’s local time or Coordinated Universal Time (UTC). For example, if the parameter value specifies 9/1/1960 5:00 AM and the local system's time zone is EST (UTC -0500), then the agent must add 5 hours to the parameter value, resulting in 9/1/1960 10:00 AM (UTC), so that the event actually happens at 5:00 AM local time.
In the Date box, adjust the date.
Select the Use Each Agent’s Local Time check box to use the agent’s local time. To use Coordinated Universal Time (UTC), clear the check box, and then select a UTC from the Time Zone combo box.
datetimeduration: Select the date and time duration by adjusting the values for Duration, Hours, Minutes, and Seconds.
datetimerepeat: Select the date and time repeat cycle (never, daily, weekly, monthly, yearly).