Can you help?

Question one.

I have issues with some script my friend is running. I know html but JS eludes me for the most part. My friend has a script that rotates linked banners when the page is refreshed. It works now that I fixed it's original problem, however, I'd like to adapt it to another function that needs to be timed... for 10 seconds (more or less) before it changes the linked banner rather than waiting for a page load.

The rest of the script works like I want it to. (By the way, this script is not random - it loads banners sequentially from a list.)

This part of the script.... what can I do to make the banners rotate without refreshing? (I know that it's teh var sec = but.... I'm I've never done this before so I'm not sure what numbers to put in - I'm sure it's not as simple as typing in a 10).

var how_many_ads = X
var now = new Date()
var sec = now.getSeconds()
var ad = sec % how_many_ads;
ad +=1;