what controller do you have with it ? The newer controllers have much more settings and you can set different day and night profiles for fan speeds
I definitely think that you should have the fan run 24/7. The cloudlines are awesome so you will be able to dim it down and not worry about heat problems that could come with non-dimmable fans being dimmed.
There will be a big improvement having the fan constantly on and as the plants grow bigger you will have to deal with more humidity and the dehu you currently have might be fine