I asked Petri this question at the Artlure seminar,he said that he has never tried klopping at night because he is usually tired at night from catching lots of fish during the day...lol
Another reason why he has not tried at night is that during winter all his klopping is done with sight fishing
He mentioned that it should work well at night during the summer with a slider or pumpkin seed and that he wouldnt vary his tactics,the barbel could be even more aggressive as this is their natural hunting time.