Not good for them, you ever been so dry your nose cavity hurts and your so thirsty your lips crack, etc...?
You can up your humidity by putting clean painters plastic on the back and sides, and putting plants in the enclosure. Not little desk plants either, a nice sized pothos and larger umbrella plant will both help hold in the humidity.
Lastly break down and buy a misting system from aquazamp or mistking. Then it does not matter if your away for 12 hrs.
Also the key on your keyboard under the Left TAB key, learn it love it use it... no need for caps lock.