I am wanting to create an app that will let a user check to see if their forum post has been replied to.

How should I go about this?

I was thinking to maybe check the content of the web page every 5 minutes. However, some pages have adds on them, so the content will change when a different add is displayed.

Should I maybe check the time of last write to a page? Will this work or will adds change the write time of the page or will the write time be only when the forum post is first created and will not be updated when a comment is replied to?