Setting Connection Timeout..

The timeout for our IIS 6 is set to 20 minutes (I think it is the
default).
We need to set the timeout to 200 minutes or more.
So I have done right click on the "default web site" in IIS, select
"properties"and set the field "connection timeout" to 12000 seconds.
Then I have done "IISRESET" and try,but the connection timeout is
always 20 minutes..I don't understand.
Can someone help me please?

Regards,
Maurizio