You can set the client.inet.cacheEntryExpTimeSec parameter in the default.cfg file to specify the number of seconds used to determine expiration time when no other expiration time is available for a cache entry. For example, this parameter would be used if the VoiceXML document does not provide metadata fields for Expires or Last-Modified in the header.
The default value for this parameter is 86400, which means that a page expires after one day.