It's not unusual for garters to be active at night or just for an early morning warm up and then again for an hour or three after dark, particularly if the temperatures are warm. During the warm summer days, garters in the wild tend to disappear after mid morning and come back out for the last couple of daylight hours. During very hot spells, they will usually become nocturnal. I've had albinos that avoid light altogether and only come out at night. Garters aren't strictly diurnal. In captivity, very cool nights (down to around 60 F or cooler throughout the tank) tends to increase their morning activity as they come out to bask and warm up. Once they've reached optimal temperature, and can maintain it while hiding, they will usually just hide unless they are very hungry and looking for food. Your snakes are being crupuscular or nocturnal simply because the temperatures at those times are warm enough for activity and darkness provides some security. I'm willing to bet that if the nights were colder, and daytime highs a bit lower, they would be more active during daylight hours.

Most UV bulbs put out much lower levels of UV than the sun does, and the UV only reaches about 18 inches from the bulb. I don't think your snake is hiding because of high UV levels. Garters don't actually need UV but I like to provide a little anyway unless they're albino. I think it has positive psychological effects on them, just like a sunny day does for a person.

As far as feeding goes, everyone's pretty much said it. Food should be neutral or cool to your touch. Sometimes they drop food items just because they don't like the mouth feel or texture. For example, I've had snakes that refuse to eat mice with hair and so will drop it. Those snakes will only eat mice that are naked. Try feeding pinkies while they are wet or dry, room temp or cooler, and see if your snake has a preference.

Most of my snakes will eat while opaque but will hide all the time during that stage and be very grouchy and easily spooked. Remember, if the eyes are cloudy, they are all but blind and therefore feeling vulnerable. After the eyes clear, but shed hasn't taken place yet, they will usually refuse food. A full belly can impede the shedding process.