Here is a small howto that will show you how to unpublish a node after a given time can be in days, in seconds … Drupal using the module Rules
First, what does the module Rules?
Rules can be viewed as an evolution of the core module and trigger is the enhanced version of drupal 6 work flowing to Drupal 5.
Rules allow to discover events, perform actions (post a comment, send an email …) automatically with the possibility of moving conditions.
Here is a small howto to un-publish content after a certain time, it could be 15 days, 30 seconds, Wednesday, Nov 09 …