I wrote a scheduling program for my sprinkler in PHP, but instead of using cron I used upstart. Upstart is cool because it actually makes it a daemon that you can start say when apache starts, and will restart it if something fails. I just put a loop in my php file that way it never ends. Plus with upstart running the PHP as a daemon you can make it check the database say every 15 seconds instead of every 15 minutes with less resources. Just my two cents 😉