crontab -e and put the below
* * * * * ( curl http://abc.com/file.php)
* * * * * ( sleep 10; curl http://abc.com/file.php)
* * * * * ( sleep 20; curl http://abc.com/file.php)
* * * * * ( sleep 30; curl http://abc.com/file.php)
* * * * * ( sleep 40; curl http://abc.com/file.php)
* * * * * ( sleep 50; curl http://abc.com/file.php)