Christopher Pike: Archiving after 30 days since the event is long over, and to keep it from continuing to appear on cacher's search lists and pocket queries. From the guidelines: http://www.geocaching.com/about/guidelines.aspx#event
After an event has occurred, the listing is to be archived by the geocache owner.
I want to thank you for the time that you have taken to contribute to geocaching in the past and look forward to seeing more of your events in the future.
Christopher Pike
volunteer reviewer