Need more info.
What kind of email:
One with server status?
One with users registered in the last hour?
A Server backup?
It is however possible to run scripts at time intervals by using "cron jobs" (on a linux server).
If you have a control panel for your server (usually is you use shared hosting) this is usually easy to setup.
If it's a dedicated server then you would have to findout how to set cron jobs on your server using command lines.
On windows it would be done a different way and i'm afraid i can't help their.