Cron php5 too many processes

I have a cron:

* * * * php5 /home/update_tunein.php
* * * * sleep 15; php5 /home/update_tunein.php
* * * * sleep 30; php5 /home/update_tunein.php
* * * * sleep 45; php5 /home/update_tunein.php

Every time cron makes a new proccess. These proccesses makes CPU usage 100%. How to make cron do only 1 proccess? Or maybe how to kill proccess after work?

... && killall php5

isn't working. Help me please