According to description of Gamma parameter, the values are only 0 to 3, But (while in layout view in C2) I personally tried values way higher than 3 like 50, 80, 100 (this looks closer to full black).
You can try a counter (using a global variable) that adds to itself every second and (for action) Set parameter 0 to a variable's value also (this variable's also being increased through time).
I never tried this btw, but I checked and there seems to be no expression for effect parameters, so you can't reference "the current parameter value then add 1" as expression (as far as I know)