Why does the Initial .NET Search Page Take Much Longer to Appear?
By default, ASP.NET Web pages are compiled dynamically when users first request a resource from a web site. After pages have been compiled the first time, the compiled resources are cached, so that subsequent requests to the same page are significantly more efficient. By default, IIS closes applications that have been inactive for some time. The next user requesting service from that closed application will experience a slow response while waiting for the initial loading to complete.
You can solve this problem by configuring CES to periodically send requests to a search application to ensure it is continuously loaded in IIS (see Pre-Loading a .NET Search Page to Prevent Display Delays).
Note: Refer to the Understanding ASP.NET Dynamic Compilation MSDN document for more information.