There are mary lights in this world, over refugiums and otherwise, that are on 24/7. EXIT lights for example are never turned off. Turning a light on and off shortens it's life. A fan might extend the fixture's life, but may be unnessisary unless you have heat issues in the tank.
Your concern about the time the light is on may be misdirected. In a refugium, it will depend on the type of Macro Algea you keep as to weather your lights should be reverse lit, or on 24/7. It is my understanding that most macros will 'go sexual' if you don't light them 24/7. Cheatomorpha being the exception.
My fuge is lit 24/7 even though I have cheato.