Special 25,
The statistics that I have seen indicate that the accident rate for offshore flying at night is about 5 times greater than that during the day, so it makes sense to avoid night passenger transport whenever possible. That said, this is likely to be very difficult to achieve during the winter at high latitudes.
I suggest that it is inappropriate to make a direct comparison with fixed wing operations, as there are fewer variables (typically instrument approaches to a well-lit runway) than in offshore rotary wing flights. I believe that good training and SOPs can be very effective in reducing the risk, but not enough to equate with day flying.