How often to replace zoomed moss (crested gecko)?

I just purchased some zoomed moss to help retain humidity in my new crested gecko's enclosure. I heat the tank using either the red 60watt bulb or heat mat and I keep damp towels on top of the screen. Humidity stays around 50-80%. I just put in the moss today and the package says to clean the moss 2-3times a week and not replace it until 3-4 weeks. How accurate is this?