Don't water again until the soil surface feels dry again. A moist soil is the safest and most desired condition for most plants. After moist, a soil becomes wet which can be tolerated by few trees. If your soil is always wet, check for poor drainage, non-functioning roots, and review your soil formulation. If your bonsai are in leaf and we have a sudden cold snap you must provide your trees with protecting from frost.
New growth is very tender.
A sudden cold spell will not only kill the new growth but can damage new root growth.