Alex, I have always tried to keep my fiddle leaf ficus plants constantly moist at all times. That is dependent on the potting soil being very open, very well draining, and having pots with adequate drainage holes. I custom make all my own potting soils (and landscape soils for that matter), so I can achieve the soil mix that I know is right for my tropical plants. That being said, the fiddle's need for moisture is so dependent on how much light she receives. It also depends somewhat on humidity and air-movement. A fiddle that get's loads of indirect sunlight will transpire far more than a fiddle that gets low light. Thus, the need for water varies greatly. For those that are sort of new to growing tropical plants inside (and keep in mind that the vast majority of our "houseplants" are tropicals), I simply tell them to look at the potting soil. If it looks like it's getting dry, water. If it looks moist, don't.