problem with progress updater using timed callback

I have implemented a system in the CMS I've developed to automatically validate links in the link library within the CMS. As the validation involves attempting to connect to every link in the collection, it naturally takes some time, so I want to have a progress updater which keeps the user informed of how the link validator is getting along. I use a timer on a page which calls a function on the server to return the link currently being browsed, and the number of the link within the total. This information is then displayed asynchronously in an UpdatePanel. This works, but there is one problem. When the "check links" button is clicked to initiate the checking process, there is a long delay before any progress update is displayed. By the time the progress update starts to work, most of the links have already been checked. I can see that the timed callback is not being activated during this pause. I'm wondering if anyone has any suggestions as to why this is occurrin ...