I have the AT&T Galaxy Note with ICS 4.04 and experience the same behavior as described below:
When I make a call using speaker mode with the phone away from my ear, the screen dims after 12 seconds and the screen turns off after 31 seconds. This happens regardless of the following conditions:
-Screen Timeout set at 1 minute or 5 minutes
-Proximity sensor turned on or off
-Power saving turned on or off
-Screen Protector installed or removed with clean screen
The only exception to the above is that with the proximity sensor turned on, if I wave my hand over the proximity sensor, the screen will turn on and the 12 second (dim) and 30 second (screen off) cycle is repeated. If the proximity sensor is turned off, the only way that I can turn the screen back on is to push the power button.