When do they croak? Do they start when they reach sexual maturity or will they croak whenever they feel like it?

When I first introduced my two White's Tree Frogs to each other they freaked out a bit, and croaked a bit. A few days ago I was squeaking my desk chair, and heard one of them croak. Today I misted my frogs with treated water- which usually makes them pretty active (hoping that means happy)- attempted to mimic a White's croak, and got a weak response from my biggest.

When I was researching frog care I was a little worried that I wouldn't ever get any sleep, but I don't think that will be much of a problem. Whether they are chatter boxes or not I'm sure it won't be as bad as when I used to have three full grown bull frogs living in my dad's koi pond 15 feet from my bedroom window. I'm a bit excited to hear them throughout the night along with my crickets~