I live in Minnesota and the beginning of winter is starting. I'm trying to get it enough sunlight, I'm kind of thinking that might be the problem. However, now that it's getting into winter the days here are usually overcast and grey most of the time. I've been putting it out for an hour or so each day, but I can't leave it out for much longer because it often drops to like 30 degrees during the day. When it's inside I have it by a large window to get partial sun and we keep the house about a constant 70 degrees. I give my tree water whenever the soil starts to feel just barely damp underneath. But the leaves have started turning a lime green color and then they fall. I'm loosing leaves daily. There are still leaves trying to grow in, but they are a light green.
If you mean, by Tea tree, Fukien tea, or Carmona microphylla, this particular one is actually an indoor bonsai. It can be stood outside in a shadyish (dappled shade) spot during the summer if the temperatures get high enough where you are, but should be kept indoors if the temperature outside falls below about 70 deg F.
Indoors, it needs good light, but not direct sunlight during summer in particular, though a little in winter is fine. It likes warm temperatures, around 70 deg F, and does not appreciate draughts, but should not be placed in a window above a heat source (like a radiator) or near any object which produces heat within the home.
I'm afraid your moving it outside for an hour or so daily and then back in won't be helping at all, in fact, its totally detrimental to the plant's health. It needs a settled, warm, bright position, it does not require sun, just bright daylight, should be fed and watered well between spring and early fall, then watered less, but still when required, during late fall and winter, and not fed again until spring. I don't know what your care regime has been regarding feeding, nor how long you've had the plant, but its entirely possible exposure to colder temperatures, and constant transitioning between in and then outdoors, or exposure to sun may have caused the problems you're seeing. More info in the link below
If your bonsai is not this particular variety of tree, then we'll need a photograph or the latin/botanical name to give better advice.