The morning!
Plants are kinda like us in that they like to be watered in the morning hours. Watering before the is good practice as when the sun starts to shine it bakes the water in the soil.
What about air plants?
Air plants such as ferns are great to mist in the mornings and on cool evenings, as they are sure to appreciate the extra humidity. For plants not thriving in dry indoor environments, evening misting may be cure to their moisture deficit.