Watering time of day is complicated. Most epiphytic orchids have succulent-like metabolism so it would be better to water in the evening if other growing conditions were good.
But in captivity growing conditions aren't like in the wild. Many greenhouses have higher day and night temperatures in summer than ideal for the orchids contained therein. People growing in hot and humid climates, like much of the American midwest, parts of Hawaii and Florida struggle with fungus attack. Orchids from even slightly higher elevations don't have this problem at home.
In conditions of lower humidity, water evaporates rapidly even at night. This also provides night cooling. During periods of low humidity and warm to hot temperatures I prefer to water my orchids in the evening, both for the cooling and because that is when they are expecting water. In periods of higher humidity, or in my hot and humid sunroom, I don't do this.
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