Basically it would be on the html side of your aspx page.
So you would browse to the page the first time, and maybe authenticate or something like that, and then the app would check if the update is completed. If it isn't, then you sent to the client the html page but with a javascript refresh - or - easier still - a META refresh.

Look up on google for doing META refreshes.

Anyway. For each requery to your page, if the update is complete then carry on, otherwise send the client back the meta refresh.
You could have in the HTML something like an image that's scrolling or changing or something to make it look like your asp.net page is actively doing some work - when all its doing is checking every 5/10/15 seconds because the browser is requerying it