Chapter 23 WAN Optimization, Web Cache, Explicit Proxy, and WCCP : Web caching and SSL offloading : Changing web cache settings : Max TTL
  
Max TTL
The maximum amount of time (Time to Live) an object can stay in the web cache without the cache checking to see if it has expired on the server. The default is 7200 minutes (120 hours or 5 days) and the range is 1 to 5256000 minutes (5256000 minutes in a year).