Julia recommends on her web site (underEstrogen dominance) to take the CB in the morning and Fem-mate at nght. I can't find anything that that suggests that you should not take CB at night but nowhere does she suggest that you do.
The Bupleurum in CB increases energy flow in the liver. My guess is that the increased energy flow might keep you awake. People who have toxic livers tend to awaken in the early hours of the morning due to increased activity and toxin removal.
I use a herbal preparation that has gentian in it but has a lot of other herbs as well and I find that better for liver detoxing than the CB. However, according to Julia the other herbs that I take can increase estrogen levels so may not be appropriate for everyone. I find that CB makes me very hungry as gentian is a bitter herb that stimulates digestion and I have a hard enough time controlling my appetite without stimulating it knowingly (LOL). I never got the same detox reactions with CB that I get from my other herbs but then I didn't really persevere with the CB because of the appetite issue.
Hope this helps but if not perhaps you should try giving Julia a call, it seems from other comments on this board that she is very helpful.