PHP: Dynamic Cron

PHP: Dynamic Cron

if(isset($_POST['matching_algo_run_time']) && !empty($_POST['matching_algo_run_time'])){
	        	
	$algo_time = explode(':', $_POST['matching_algo_run_time']);
	$hours     = $algo_time[0];
	$minutes   = $algo_time[1];
	$hour_12   = ($hours > 12) ? ($hours + 12) - 24 : $hours + 12;

	if($hour_12 == 24)
		$hour_12 = '00';
	
	$output    = shell_exec('crontab -l');
  $cron_file = '/tmp/crontab.txt';

    if(file_exists($cron_file)){
    	unlink($cron_file);
    	echo exec('crontab -u www-data -r');
    }

    $cron1 = "$minutes $hours * * * curl -s -m 10 http://localhost/one_degree/admin/welcome/send_email";
	
    $cron2 = "$minutes $hour_12 * * * curl -s -m 10 http://localhost/one_degree/admin/welcome/send_email";
    
    file_put_contents($cron_file, $output.$cron1.PHP_EOL.$cron2.PHP_EOL);
    echo exec('crontab /tmp/crontab.txt');
}