Running a PHP script on an automated regular schedule

Hi. I am wanting to use a PHP script to check on an hourly/daily basis on a few things- ie links on my sites, whether the sites are up and running and also to send an e-mail to me. I know how to do this using PHP but my problem is how to have this running 24/7. I can't really have this on a web page as wouldn't it time out? I don't have my own server and so use a hosting company. Is there a way of running a PHP script on a regular basis (say every 10 or 30 mins, or hourly or daily)? Would I have to set up my own server to do this? I just the simplest way of acheiving this. Any ideas? Does anyone know of any decent link checkers written in PHP that I could implement? Many thanks, Ian Gray