A partir do FAQ do CloudFront :
Q. How long will Amazon CloudFront keep my files at the edge locations? By default, if no cache control header is set, each edge location checks for an updated version of your file whenever it receives a request more than 24 hours after the previous time it checked the origin for changes to that file. This is called the “expiration period.” You can set this expiration period as short as 1 hour, or as long as you’d like, by setting the cache control headers on your files in your origin. Amazon CloudFront uses these cache control headers to determine how frequently it needs to check the origin for an updated version of that file. If your files don’t change very often, it is best practice to set a long expiration period and implement a versioning system to manage updates to your files.