Every time I take my frog out to feed or to spot clean or for any reason.
I use this time to add treated water to the substate to get it to the level of clumping when compressed and not sopping wet.

With doing that and the amount of cover I have on the top screen it keeps the humidity levels around 70-80%
and if drops below 70% the Hygrotherm kicks in the zoomed reptifogger but that is a rare thing.
I normally don't have to refill the bottle for month to more.