I would like to execute a PHP-script automatically on a timestamp defined time.  

So lets say I have calculated a future-timestamp (e.g. 1359504000) in another PHP-script and exactly at this time (something like) a cronjob should call the other script. afterwards it (I am thinking about conjob currently) should be disabled/killed/deleted. 
What would be the best way to do this type of task?
thanks!