Linux tip: Job scheduling with cron and at

"You need to run a job at midnight when system usage is low, or you need to run jobs daily or weekly, but you would rather be sleeping, or enjoying life in some other way. Other good reasons for scheduling jobs include letting routine tasks happen automatically, or ensuring tasks are handled the same way every time. This tip helps you use the cron and at capabilities to schedule jobs periodically or at a single future time."

http://www.ibm.com/developerworks/linux/library/l-job-scheduling.html