Magento

I’m not familiar with CRON job feature.
I would like to know How can I export my customer by using a cron job.
This cron job will do this :
1-call a export profile
2-do some modification on it (filter on the creation hour for example)
3-execute profile
4-zip file
...

I need help on the part 1-2-3. Even somes indications will help me

Thanks

No one ? :(