Enough to keep the leaves wet for 2 hours(30sec to 10min sprinkles depending on cage,heat,humidity), and and leaves are fully dry before the next misting. Also dont have it go off before bed, you want a dry night, or yull get upper respiratory problems in the long run.
Normally misting is 3-5 times a day with the automated systems. The key is rain, dryout, repeat.