Do my oscillating fans need to be on all the time?

Yes, you should have your oscillating fans on all the time. The oscillating fan simulates wind making the plant stronger. If the fan is not on all the time you are risking the plants getting moldy. HOWEVER, do not have the fan blowing so much that the plants look like they are in a wind tunnel as the plants will get wind burn which is permanent leaf tissue damage. The leaves should just barely move as the fan passes them.