put
int startCounter= DateTime.Now.TimeOfDay.TotalSeconds;
as a first statement in the page_load in order to to get the TotalSeconds when this application has been loaded
and at the end of the page load add
int endCounter = DateTime.Now.TimeOfDay.TotalSeconds;
now add
int totalSeconds = endCounter - startCounter;
//which will get the time needed to run this event.
Response.Write(totalSeconds);
Also Refer This Link
http://msdn.microsoft.com/en-us/library/0x5wc973(v=vs.85).aspx[
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Hope This Will Help You