How would I go about adding a Queue like ticket master?

To make my question a little more clear, I am trying to set up a queue to manage traffic to an application on the server that only accepts 250 concurrent users at one time. How would I set up the redirect on the load balancer to redirect the first user that exceeds the 250 concurrent users to a page, for example, that would say "Your request cannot be executed at this time".

 

 

I would like to build a script to keep checking the status of the application. If the script finds that the concurrent user level has dropped, then the user would be redirected to the application's webpage. Two ways that I thought of doing it would be 1) have a please wait page that loads the page in the background and 2) put a sleep timer on the script to loop through the execution every 2 minutes for example. Anyone have an idea?