Update CCK Field Every 90 Days I'm using Drupal 7. I have a CCK field called Placement Date (Placement_Date) that the end user will manually put in. I then have two text fields, Start_of_Period and End_of_Period. Start_of_Period initially is set to Field->Placement_Date and Field->End_of_Period is set to 90 days out. The setup is no problem, but after 90 days Field->Start_of_Period needs to be the old End_of_Period + 1, and Field->End_of_Period needs to be another 90 days out from the new Field->Start_of_Period. I looked to Rules to try to find a way to schedule this, but cannot figure out what I need to be doing.

Any help would be greatly appreciated. Thanks in advance.
You need to set up cron tab on your server may be once a day
  use hook_cron() to add your custom code write query to grab nids for which field values needs to be updated.
  use node_load_multiple() to load all nodes with the query returned nids
  update the field values and save the node again in a loop.
  set the crontab to run at the time when your site receives least traffic, this way it will not be performance issue as well.