Preferences

Dimmer's functions are controlled from its Preferences Panel.  You can chose the idle time before dimming interval from 1 to 30 minutes (it defaults to 3 minutes) or turn dimming off altogether.

You can also chose whether or not you want it to play Westminster Chimes, and, on a scale from 1 to 100, how loud it will play (it defaults to 25).  The "Sample" button will  play the first note of the chime at the currently selected (but not necessarily set) volume level.

For visual stimulation in the guise of useful feedback,  the application icon's monitor screen dims from red to black as the time to dim approaches.