Thanks for all the input - but I really only wanted some advice on the UVB bulb-to-turtle distance. I've kept box turtles for nearly 40 years, so I'm not a novice. I've dug up nests and incubated, I've left them in the ground to fend for themselves, and I've dug, hatched, and released some and kept others inside for their first winter. I just haven't used a UVB bulb on them before - they were not widely available in the distant past.

Anyway, as soon as they start hatching, I'll shoot for a 12" distance at one end of the box. I kind of miss them when they hibernate over the winter, so this will give me some young ones to fool around with during the bleak days of cold and gray.