How to execute a scheduler at a random interval?

There is a scheduler, Prune Old Record Lists, 
https://support.sugarcrm.com/documentation/sugar_versions/13.0/serve/administration_guide/system/schedulers/#Prune_Old_Record_Lists

which executes As Often As Possible. This scheduler will execute "optimize table record_lists" every 1 minute. 

function cleanOldRecordLists() {
    global $timedate;

	$GLOBALS['log']->info('----->Scheduler fired job of type cleanOldRecordLists()');
    $delTime = time()-3600; // Nuke anything an hour old.

    $hourAgo = $timedate->asDb($timedate->getNow()->modify("-1 hour"));

    $db = DBManagerFactory::getInstance();

    $query = "DELETE FROM record_list WHERE date_modified < '".$db->quote($hourAgo)."'";
    $db->query($query,true);
    $db->optimizeTable('record_list');

	return true;