I mean the answer obviously depends on what the road is like. Near me, for example, I have 2 different roads that I drive on most often at night, both with speed limits around 35-40. One of them is in town, and has streetlights, stoplights by the crosswalks, and is just generally way better lit. Even so at night visibility is worse, so I’ll go like 10 below the speed limit (maybe only 5 bit depending on if I don’y see/think people are out walking or if I’m not as worried about visibility). The other road is basically a country road. It has trees and farm fields on either side, no lights, and is extremely hilly. Because of all that I go like max 20 or 25 pretty much, so I have enough time to brake for a biker I missed when I went over a hill, or for a deer or other animal that jumps out in front of me.

The dangerous thing in a crash between a bike and a car is definitely the car, so it should also fall more on the car to be safe. Not to say a bike has no responsibility for their own safety obviously, but a car should be traveling slowly enough that they have the ability to stop without hitting something if they have a sudden need to, and that means potentially going much slower than the speed limit at night.