I try not to comment on systems that I am not sure I can give a good answer to but... many of the Clack valves are not adjustable other than their pre-set parameters, or "hi" and "regular" settings. I am not sure of the Greenway, but I would guess that could be your problem. It may not be adjustable. BTW, I have worked on a few of those units in the field, they are excellent systems. Many of the Clack proprietary valves are programmable. So my answer means nothing. Let me know when you find out from Greenway if the times are fully adjustable. Thanks!