Actually, you don't want it wet in there day and night. What I have found through research is that you want a period of drying out (relatively, of course)
What was suggested to me is to mist once or twice in the daytime. Then allow for the cage to dry during the evening/night. Also, you don't want the sides of the cage continuously wet, as that is too humid.
I believe that that is why there isn't a "set number" for the humidity level out there. A cycle is a better way to put it, although you can keep the humidity continuously high during a shed cycle I believe!
Good luck,
Brent Strande
P.S.
Here is an excerpt from Greg Maxwell's site ( www.finegtps.com ) located here:
http://www.finegtps.com/Care_sheets.html
Humidity
This is an important topic when discussing chondro husbandry, and is one that causes unnecessary confusion. The level of humidity in a given environment will be based on a number of factors such as how much moisture is added to the cage daily, temperature, ventilation, how well the cage substrate holds and releases moisture, etc. You will need to experiment with your own set up and existing factors, adjusting these until you have the correct balance. Use observation as the best guide, which is better than attempting to maintain a specific percentage of relative humidity. Also, remember that just having a wet cage interior is not the same as providing humidity, which is the amount of moisture in the air. For example, an excessively ventilated cage can have standing water on the floor and still not be humid.
Many people have an exaggerated idea of how much humidity these snakes require. They may suffer health problems if kept too wet, including skin infections. The only time to err on the wet side is during the animal’s shed cycle. Chondros are very thin skinned and sheds will dry on them very easily if the relative humidity is too low during the shedding period. The goal should be a gradual drying out period at night and early morning, followed by an increase in humidity in the afternoon and early evening. Condensation on the glass 24 hours a day, or the growth of mildew or mold, indicates excessive humidity. On the other hand, if the cage is dry three hours after spraying, there is not enough humidity. A hand-held mister or pressure sprayer works just fine for daily misting. I have used automatic misting systems and do not care for them. Another important point to remember is that chondros may drink off of themselves after misting, so keep the water and the sprayer clean!
To sum up...provide moderate to heavy humidity, along with an overnight drying out period. Regulate cage humidity by increasing or decreasing the amount of misting and dampness in the cage substrate, along with adjusting the ventilation. And remember, other than at shedding time, humidity is not critical. Getting it right is important to the long term health of your animals, but having it too high or too low for brief periods won't hurt anything.