From the documentation of SQS, Max time delay we can configure for a message to hide from its consumers is 15 minutes - http://docs.aws.amazon.com/AWSSimpleQueueService/late
Visibility timeout can do up to 12 hours. I think you can hack something together where you process a message but don't delete it and next time it is processed its been 12 hours. So a queue with one message and visibility timeout of 12 hours. That gets you a 12 hour cron.