We have procedures that take a long time at work...sometimes to the the tune of an hour or two. When it goes on for that long, your browser will time out the HTTP request. How we get around it is to start off the process in its own thread then present the user with a "wait" page that sends off requests now and then to see if the process has completed. Once it has we redirect them to the page they need to be at.
This can be accomplished with straight browser refreshes after x amount of seconds or through asynchronous requests back to the server to check (my preferred way because you don't get annoying screen flickering as the web page refreshes itself and you have to send back a lot less data through the connection to verify the status of the long process).
Locking the browser waiting for a request is generally a bad thing because the user has no idea as to what is going on.
The added benefit of sending off periodic requests is that if you have any sort of session management timeout, this will renew the session while the long process is happening.