Normally, the CAM orchids have a thick, rough leaf and pseudobulb such as Aranda, Aranthera, Caliente, Cattleya, Coelogyne, Dendrobium, Laelie, Phalaenopsis, Thunia and Vanilla. They have an ability to keep the water in their leaf or stem. So, they can bear to hot weather than thin and smooth leaf such as Arundina (C3 orchid).
Smooth leaf orchids start Co2 fixation when they are under the light. So, you should water them before 9.00 AM. But CAM orchids start Co2 fixation when they get a high humidity, their stomata will open after 06.00 PM. This is a good time to watering CAM orchids. However, some CAM orchids require an additional watering before 7.00 AM.
The frequency of watering is also depending on your humidity and planting material. When the plants don’t have enough water. Their leaves will be yellow and withered. You should spray water until the stem, leave and root are wet. One time a day or two times a day in dry and hot period. The leaf sheath should dry in 3 hours. And if your planting material can absorb much of water such as sphagnum moss, you should spray water every 3-5 days.
Quality of water is important. Watering them a lot with good quality water, less watering when you have poor quality water. This concept should be in your mind.
REF: ว่าด้วย กล้วยไม้: ศาสตร์และศิลป์ เพื่อการพัฒนา