Question on watering mounted Phals.

[Kai]

In a few days, (when I receive the cork bark I ordered) I'm going to be mounting a smallish phal. It will be my first time trying to mount, and I've been doing a lot of research. But I haven't been able to find anything about how dry I should let the mount/moss/roots get between waterings. The plant will be in an area with 50% to 60% humidity, though I plan on adding a cool mist humidifier to the area. Thanks in advance.