The following very useful piece of advice is by Michael Hagedorn from his website Crataegus Bonsai.
Last summer I mentioned the practice of ‘hamisu’ which is the misting of bonsai during hot summer days. This light topical watering wets the foliage, trunk, pot and first half inch or inch of soil. It refreshes the tree.
If you water the trees in the morning on hot days, they will often need this lighter watering once or twice following that. This is especially true when the temperatures rise above 90 degrees F. Hamisu is most effective when the sun is lowering in the sky.
Be careful watering too late in the day when you have fungus problems. There is juniper tip blight, Phomopsis, to be concerned with, for instance. Any water on the foliage should dry before night sets in during the warm months.