Here is a frequently asked question: why can't I see IIS logs written immediately after a request?
The anwer is that the HTTP.SYS buffers the IIS logs and flushes to the disk every 60 seconds because of performance issues.
If you are running IIS 7.0 or IIS 7.5 and if you want to flush the HTTP.SYS buffer to the disk immediately, you can open a command prompt and run the following command:
netsh http flush logbuffer
Applies To: IIS 7.0, IIS 7.5