Fans on 24/7 or off during dark period?

The Only time i turn off my fans is 20 min before day "lights on" to give them a cool down only for the motors. Plus ive herd that plants highest Out Put of Co2 is right before day. But other than giving them a small break, there on all the time.

hope im right

temps are gonna drop so A/C shouldnt be problem at night, however a fan should always be on, helps strengthen the stems.