if this script creates some output for your vistors, u might write a little script that stores the last generation date and passes through the data u generated once - now, u check everytime someone visits your page whether time()-$lastUpdate > 606024, i.e. one day - if so, u gotta recreate your data - it's not a real cron job, but at least an approximation if u do not need a precisely set time when to call your script.
hth