Hi.. I harvest during the 'day' time. Since it usually takes up to a week to get everything trimmed and ready for drying, I don't like to interrupt the day/night cycle. But I really don't think it matters much, as the other posters have said. Hope you have a great harvest!
A lot of books and experienced growers suggest cutting it down right before the lights would come on, at the end of the darkness cycle. The reasoning behind this is because the plant moves nutrients and shit down to the root system for night and it is distributed back into the leaves when the lights come on, so chopping it at the end of the darkness breaks it away from that buildup in the roots. Several grow guides suggest this. But I truly don't think your gonna be disappointed even if you harvested in the middle of the light cycle. But this does seem to make sense, and would help with curing. good luck