These warm summer days (that we are not blessed with too often this summer), it is important to provide some partial shade for especially smaller bonsai. Small shohin bonsai are easily dried out during a warm day, and partial shade in the middle of the day is essential in midd summer. Use a net for the purpose, or place the bonsai under partial shade from large garden trees for example.
Check regularly for watering needs during the day when possible. Bonsai do not dry out at the same time, just because they have the same size. Different leaf amounts and different types of foliage decides how much each plant evaporates. Weaker trees with less roots have to be shaded more, because the fewer roots may not be able to take up enough water to follow the speed of evaporation.
Please also take in mind the importance of the pot quality. The classic Japanese and Chinese pots are made especially to fulfill the purpose of being able to keep the roots cooler. Some western pots are made of heavier clay, and build with thicker walls, not having the ability to keep the temperatures low in the pot on a hot day with sun heating up pot, soil and roots. It is essential to keep the trees healthy avoiding an overheated pot. In nature the roots of the trees are always deep in the soil and kept in a natural steady temperature. Bonsai lives a more dangerous life, where soil temperatures vary when heated by the sun and cooled by watering. Good bonsai pots build with the right clay and thinner walls helps keeping the soil temperature variations as small as possible.
Finally. Do not wait to the afternoon to water your trees if they are dry. Water immediately and when needed. Harmed roots dried out and overheated may damage the health of the tree severely.