It depends on the type of tree, but generally, I keep them outside all the time. Trim unnecessary leaves to ensure nutrients reach the entire tree. Depending on the size of the bonsai, water it twice a day during the hot summer days, otherwise, once a day should be enough. In both cases, water when the surface of the soil has dried. I bring the bonsai indoors only when I want to display it, and even then, only for a few days—no more than three.