The Milwaukee has a body unit that has the settings and reading of what the probe is sending for PH. Then there is a "pigtail" item where the solenoid is plugged into power. This acts like an outlet which is switched on/off by the controller. So one can set the PH on the controller, plug a solenoid into this switched outlet and let it come on/off as the PH moves. This keeps PH steady. Or one can add a timer on the solenoid and have both the timer and the controller maintain the PH. To me, this seemed redundant and I really see little value in adding swings in the PH to save a small amount of CO2 used overnight to keep the swings lower. I save the added complexity of the timer ( they tend to get off on time more than I like) and just go with being happy to have steady PH, day and night. In some tanks, CO2 is lost faster than other tanks and the swings might be pretty big, but that is a question on how each of our tanks operate. I like stable and I'm willing to go with any slight amount of extra CO2 used overnight to keep it there rather than shutting off overnight and then pumping extra when the timer comes back.
Neither method is wrong, just I like to keep it stable as well as simple, when possible. I hate finding I've screwed things up when I forget to reset timers.