I'm a firm believer that there are innumerable ways to run a reef and I'm assuming you mean lighting macro algae in your refugium. That being said, I think the argument for running opposite your DT light schedule is to keep photosynthesis occurring within the reef more constant to decrease the extent of pH swings. When I first started, I ran my refugium light 24/7 because I had the nutrients to feed my chaeto, I wanted to increase my pH as much as I could, and I didn't have another timer handy to run it opposite my display lights. I still want my pH to be higher but I have changed my refugium light to opposite my display lights because I have noticed my chaeto melting a little. I'm implementing other methods to increase my pH like running a CO2 scrubber and pulling air from outside. My suggestion would be to run you refugium light as much as you can without it melting your macro algae as long as you 1) have nutrients you want to export and 2) aren't looking for more stable pH readings throughout the day. If you need to cut back your daily lighting hours, have your refugium light off while your display lights are on. This is probably how a lot of folks that run refugiums for nutrient export got to lighting their refugiums opposite their display lights.
