Two kinds of Bonsai
Generally speaking, bonsai are one of two types, tropical and temperate. Tropical bonsai, such as serissa, ficus, or bougainvillea can not adapt to freezing temperature and must be protected against frost. (I leave my tropical out for the first frost or two if they’re not too severe) the plants appreciate the brief “dormancy Temperate bonsai ( junipers, maples, etc.) can survive lower temperatures, but because of the shallow root system, generally need some protection from the cold (I dig a two feet deep pit and cover it with a PVC frame and white plastic; not pretty, but functional).
Temperate bonsai need a dormancy period and will just peter out if you try to keep them like tropical. People often refer to tropical as “indoor” bonsai and temperate as “outdoor” bonsai, but I dislike this terminology as it gives the impression that is o.k. to keep bonsai indoors year round if it is a tropical.
Bonsai should be outdoors at all times they are able to handle it. It is all right to bring them in for a day or two to show, providing they get decent light and more water than usual, but in good weather ALL your trees should be outside.
In the cold months the tropical need to come indoors to that bright window and religious watering, the temperate can go in your frame (or similar set-up; a friend in New Jersey keeps his under his deck and I have seen them over-wintered in a open cardboard box with a layer of leaves over the pot in milder areas) and the watering requirements drop to once a week or so (if it warms up even temporarily, you should check more often.)
Acquiring a bonsai should be thought of as getting a pet plant. It needs the same continual feeding, watering, and grooming that a puppy would need, but the tree can’t whine at you when it’s thirsty or hungry, so it requires a strict schedule to maintain optimal health. Much like a good pet, bonsai can be a good companion for decades and if well kept should outlive you! (and they don’t go on the carpet…)