Its down to two uses:
Use one is to keep humidity up, either during the day or at night. These mistings are normally only 30-60 seconds. You time it so that the cage dries out between mistings so you dont get mold. These mistings are not for cham drinking.
The second use is for "rain" to get the cham to drink. These are several minutes long, and its to stimulate the cham to drink for those that only drink rain and wont drink off leaves. these are only a few times during the day. And like the previous use, you need to have the cage dry out between mistings.
I have mine setup for a early AM 5min rain(its my alarm clock), another at noon, and i final one around cham bed time(1-2 hours before lights out). I will then adjust the short mistings just to maintain humidity, and it changes through out the year.