set specific time to cron for specific php script
Set system cron to every 5 minutes, and use Elysia Cron to manage particular tasks:


  Elysia Cron extends Drupal standard cron, allowing a fine grain control over each task and several ways to add custom cron jobs to your site.
  
  
  [NEW IN 2.0] Set the timings and frequencies of each cron task (you can run some jobs every day at a specified hour, other only monthly and so on...). For each task you can simply choose between some frequently used options ("once a day", "once a month" ...), or use a powerful "linux crontab"-like syntax to set the accurate timings. You can even define your frequently used options to speed up site configuration.