Using a long setTimeout

Using a long setTimeout

i am trying to understand the  setTimeout function...
i want an ajax call to go out every 30 minutes but i want to understand the resources being spend while 
it runs in the background...

so... 
1. when a setTimeout runs does it use a lot of resrouces?
2. would those resources run on the server proccesor or the browser itself (user computer)?
3. is there a better way to tell jquery / javascript - wait for 30 minutes and why.