Setup Cron Option

I'd maybe suggest using a select for the time period as core module tend to, this is lifted from aggregator;

  $period = drupal_map_assoc(array(900, 1800, 3600, 7200, 10800, 21600, 32400, 43200, 64800, 86400, 172800, 259200, 604800, 1209600, 2419200), 
 'format_interval');
  $period[0] = t('Never');

Also it makes a lot of sense to slim the module files themselves as much as possible as they're always loaded into memory. Every little helps so would recommend moving out the admin functions to a separate file, e.g. "panels_pane_report.admin.inc" with a reference in hook_menu.

Looks great, thanks! +1