Difference in time-taken in IIS and ASP.NET

I'm developing an ASP.NET (3.5) webservice application, hosted on IIS6/Win2003. The webservice logs the timestamp of the call at start and just before the return. This allows me to query the time-taken. I've also added time-taken to the standard IIS log (W3C extended) The webservice is then stress-tested (5 threads, 200 calls per thread) When comparing the time-taken from IIS with the timetaken in the datase, I see HUGE differences! The time-taken from IIS (which is also the time-take logged by the calling clients) is much higher than the time-take logged by ASP.NET. For example, the time spent according to ASP.NET is 1.7 secs, while IIS logs 12000 (miliseconds)! What could be a cause for this? Dummy-code for the service: ``` [WebMethod(Description = " Main entry point to the service.")] public string MethodA(string theXmlInput) { //log first StoreInput(theXmlInput); //Run the job, should take about 1 sec string result = DoIt(theXmlInput); //log output StoreResult(result); return result; } ```