I have a cron job that runs every 10 minutes and updates the content-type and x-amz-meta. But since yesterday it seems like after the cron job run, Amazon is not picking up the
Use Invalidations to clear the cache, you can put the path to the files you want to clear, or simply use wild cards to clear everything.
http://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/Invalidation.html#invalidating-objects-api
This can also be done using the API! http://docs.aws.amazon.com/cloudfront/latest/APIReference/API_CreateInvalidation.html
The AWS PHP SDK now has the methods but if you want to use something lighter check out this library: http://www.subchild.com/2010/09/17/amazon-cloudfront-php-invalidator/
user3305600's solution doesn't work as setting it to zero is the equivalent of Using the Origin Cache Headers.