Time to live (TTL) is mechanism that limits the lifespan of data in a computer or network. In HTTP, TTL is expressed in the response header as a date and time on which a record expires.
On Amazon Cloudfront, the default TTL is 24 hours. In April 2010, Amazon Cloudfront announced that it will honor shorter TTL’s down to one hour. The HTTP header can be set in the Amazon AWS Management Console.
To refresh a specific file on Amazon Cloudfront, you can use the Invalidation API. The Bucket Explorer has a UI that makes Invalidation pretty easy. Informations about an Amazon CloudFront – PHP Invalidator are availble at the subchild website.