IIS Profiling - need to find the execution time of webservice methods

It depends on how you define the execution time. If you cannot modify the service, you cannot get pure server-side time. You can observe the time including HTTP transport on the client side, but this is trivial. Just time the interval between sending HTTP request and receiving HTTP response. To exclude most of the client-side time span, you can create a request on low level using the class System.Net.HttpWebRequest:
http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest.aspx[^].

The most precise way of timing is using the class System.Diagnostics.Stopwatch:
http://msdn.microsoft.com/en-us/library/system.diagnostics.stopwatch.aspx[^].

For more in-depth understanding of Web service profiling, please see this article:
http://www.netsoft-usa.com/en/HowToArticles/WebServiceProfiling.aspx[^].

—SA