You're talking about a fan on your intake? Do you have an exhaust fan as well? If you have an exhaust fan that is running then you may not need to run an intake fan all the time -- many growers just have passive intake as it is.
You want the exhaust pulling all the time. Passive intake is good. If you have an air scrubber the negative pressure will help with odor control.
If you are concerned about odor control and have filters or scrubbers inplace then yes leave the fans on or at least a few If you have no odor control then having the fans on during night hours is a waste of electricity since the plants breaths through the roots anyways GL
I leave one of my exhaust fans on all the time for the draw of fresh air, with all the humidity and residual heat from light and small spaces.Mold? Fresh air is GOOD