how to run cron hook after a week i have created a module to hook Drupal cron system and the function in my module is being executed on every cron run, which is perfect.

I need this hooked cron function to run only once weekly without scheduling the default Drupal cron job .
Any help on this ?
Thanks
Check out the variety of cron modules that set intervals, like Elysia cron.

https://www.drupal.org/project/elysia_cron