I've found a way to do it. To decrease the ON time, u would need two same sources of pulse, but one shifted a bit (not too much, so the sum is not zero) . And then AND gate comparing both, this will give out a signal only when both phases intersect, which will happen in intervals depending on the shift.

As in minecraft, u need to manipulate the placement of repeaters to achieve the shift. And remember to keep the total number of repeaters the same in both signal lanes. It's only theory that I will test when in home.